A Stochastic Model for Cell Repair Based on Enzyme Kinetics

A new stochastic model for the repair of radiation-induced cell damage based on enzyme kinetics is proposed. The model not only accounts for the depletion of enzyme level with successive repairs but also takes into account the synthesis of new enzymes in response to repairs. The cell survival probability is explicitly calculated, using which comparisons with related models are made.

Mining of simple sequence repeats in the Genome of Gentianaceae

Simple sequence repeats (SSRs) or short tandem repeats are short repeat motifs that show high level of length polymorphism due to insertion or deletion mutations of one or more repeat types. Here, we present the detection and abundance of microsatellites or SSRs in nucleotide sequences of Gentianaceae family. A total of 545 SSRs were mined in 4698 nucleotide sequences downloaded from the National Center for Biotechnology Information (NCBI). Among the SSR sequences, the frequency of repeat type was about 429 -mono repeats, 99 -di repeats, 15 -tri repeats, and 2 --hexa repeats. Mononucleotide repeats were found to be abundant repeat types, about 78%, followed by dinucleotide repeats (18.16%) among the SSR sequences. An attempt was made to design primer pairs for 545 identified SSRs but these were found only for 169 sequences.

Marker-aided genetic divergence analysis in Brassica

Genetic divergence was evaluated in 31 breeding lines from four Brassica species using Mahalanobis' D2. A new method of grouping using D2 values was used to group the 31 lines, based on diagnostic morphological traits (called morphoqts). Isozyme variation of the individual enzymes esterase and glutamate oxaloacetate was quantified by five parameters (called isoqts) developed earlier. Grouping by the same method was also done based on the isoqts, and the grouping by isozymes was compared with that by morphoqts. Overall, there was an agreement of 73% suggesting that isoqts can be used in the choice of parents and also first stage selection of segregants in the laboratory. It was suggested that such an exercise would help to take care of season-bound and field-related problems of breeding. The new isozyme QTs, within lane variance of relative mobility and relative absorption, accounted for about 50% of the total divergence. The utility of the new method and isoqts in cost-effective breeding were highlighted.

Optimal analytical conditions for catalase in fresh water prawn, Macrobrachium malcolmsonii

The cytosol of hepatopancreas was prepared from the freshwater prawn Macrobrachium malcolmsonii, and optimal assay conditions, ie., concentration of substrate, pH, and temperature, were determined to measure basal activities and kinetic constants of catalase activity. The properties of catalase were examined in M. macolmsonii, because quantitative data on catalase are limited in crustacean species. The optimal pH for catalase was 7.0. The activation energy was 3.55 Kcal/mol and energy inhibition value was 5.16 Kcal/mol. The value of energy inhibition is higher than that of energy activation. This may be due to inhibition of catalase by some substrate other than H2O2. A Km of 66.6 mM was also determined from various concentrations of substrate.

Simulations of aerosol aggregation including long-range interactions

Current understanding of solid aerosol particle aggregation is limited to simulation models based on diffusive and ballistic motion of the colliding particles. The role of the long-range van der Waals forces in aggregation phenomena, although important, has never been examined. In an effort to address this issue, a simulation model, based on molecular dynamics techniques, is developed. Using this model to simulate thermal collisions of single spheres with small aggregates of similar spheres, we examine the effects of retardation of the long-range van der Waals forces, particle transport, ambient temperature, and pressure on the collision rates and mass and structure distributions of the aggregated particles. The model calculations were performed at simulated temperatures of 293 and 1500 K and at simulated pressures of 760 and 3040 torr for glassy carbon primary particles in the free molecular regime with diameters of 6 nm, and in the transition regime with diameters of 30 nm. Inclusion of the long-range van der Waals forces resulted in aggregates with relatively open structures and few branches and collision rate constants that were larger than the corresponding hard sphere rate constants, whereas exclusion of the forces resulted in compact structures with more branches and smaller enhancements in the rate constants. The above effects were found to be more pronounced in the free molecular regime than in the transition regime, which is consistent with the observation that the initial conditions and the interparticle forces play a more significant role in particle transport in the free molecular regime than in the transition regime. The effect of retardation of the forces is an increase in the percentage of open aggregates and the collision rate constants over that of the corresponding nonretarded case. An increase in temperature resulted in a collapse of aggregate structure and a decrease in collision rate constants corresponding to the reduced geometrical cross sections. Again, the effects were found to be more pronounced in the free molecular regime than in the transition regime. No significant difference was observed in the structure of the aggregates or in the collision rate constants with a change in pressure, indicating that the pressure effect, if any, is hidden by the much stronger effect of the long-range van der Waals forces.

Comparative shoot regeneration in diploid and amphidiploid Brassica species and their interspecific hybrids

Shoot regeneration response in interspecific hybrids of Brassica species were assessed in relation to the diploid pollen parents and amphidiploid female parents. Superior regeneration responses were observed in interspecific combinations of B. carinata and B. nigra (BBC), B. juncea and B. campestris (AAB), and B. napus and B. campestris (AAC). Though synthetic B. napus regenerated with a frequency less than that of the better regenerating parent (B. oleracea), higher regeneration response was observed in the hybrid between B. napus and B. campestris. Two triploid combinations of the genetic constitution ABC, one obtained by crossing synthetic B. napus with B. nigra and the other by crossing natural B. juncea with B. oleracea, showed low regeneration responses. The response improved substantially in a tetraploid of the constitution ABBC obtained by crossing B. juncea with B. carinata. Key words: Brassica, alloploids, shoot regeneration.

Nonparametric approach to multitrait selection for yield in groundnut (Arachis hypogaea L.)

Eight characters related to nitrogen fixation and pod development measured 30 days after flowering were evaluated for their correct grading of the relative yield performance of 17 genetically diverse lines of groundnut (Arachis hypogaea L.). Each line was assigned a high or low yield status based on its pod yield, shelling percentage, and 100-kernel weight. Seventeen character combinations were examined for their relative merit in correct identification of the yield status of lines. The character sets, nitrogenase activity alone or in combination with nitrogen percent or shoot weight identified the status of 77% of lines correctly. The extent to which various characters accounted for the variation in pod yield was also checked by multiple regression analysis. While the character combination, nitrogen percent plus leaf area explained 75% of variation in pod yield, nodule mass, nitrogenase activity, and leaf area occurred in some other combinations that explained yield variation to a lesser extent. These analyses point to the profitability of involving crop physiological traits such as leaf area and nitrogen percent in selecting for relative yield performance in groundnut.

Enhanced cross pollination to widen the scope of breeding in groundnut (Arachis hypogaea L.)

Six groundnut genotypes belonging to the Virginia and Valencia sub-groups were irradiated with gamma rays at doses of 5, 10, 15 and 20 kR, much below LD50, and grown surrounded by a pollen parent in a split-plot design. The succeeding two generations were checked for the occurrence of hybrids by examining the segregation for pod and seed characteristics and the two quantitative characters, pod and seed yield. Cross-pollination up to 20.8% was observed in 'M13', a Virginia cultivar. There was a genotype-dose interaction for the extent of cross-pollination. Cross-pollination was higher in Virginia than Valencia genotypes and more frequent under 15 and 20 kR than under other doses, in general. The observed substantial enhancement of cross-pollination encourages the use of seed irradiation at proper doses as a method for increasing recombination in plant breeding programmes.

Early generation intermating for yield improvement in groundnut (Arachis hypogaea L.)

Seeds of 4 crosses of groundnut (Arachis hypogaea L.), 'Robut 33-1' x 'Chico', 'Robut 33-1' x 'NC Ac 17090', 'Robut 33-1' x 'PI 298115' and 'MK 374' x 'GAUG 1', were irradiated with 30 kR. In the F1, some branches of each plant were intermated with other plants at random and others selfed in each cross to produce S2 and F2 seeds. They were evaluated for pod yield, shelling percentage and 100-kernel weight. The frequency of plants superior to F[in1] was much higher in S2 than in F2, which was, in general, true for the values of yield and its components. The S2 and F2 were advanced to third generation by selfing. The families descending from S2 showed clear superiority over those from F2. The reason for such superiority was suggested to be the recombination of genes from the upper and lower ends of the genotypic distribution under intermating.

Efficient selection intensity in early generation index selection in groundnut (Arachis hypogaea L.)

The F2 potential of single and three-way crosses was evaluated using a set of physiological and yield components. Results were based on an index of selection using (a) only yield components and (b) both physiological and yield components. The indices were constructed using the percentage improvement of F2 over the better parent of the corresponding F1 cross for every character. The performance of F2 plants assessed by the expected value of the regression index was ranked in descending order to provide a ranked F2 distribution (FRD). The FRD was divided into four equal parts, T25 (top 25%), T50 (26-50%), T75 (51-75%) and T100 (76-100%). F3 families derived from F2 plants in T25 were found to provide a higher frequency of selections for pod number than T50, T75 and T100. The frequency of selections was higher in three-way than single crosses. Selection index based on physiological and yield components was more efficient in trapping F2 plants providing selections in F3 than the index based on yield components only. The results brought out the importance of bunch x bunch crosses as a complement to the usually advocated bunch x runner ones.

Are "multiple Cross-multiple pollen hybrids" an answer for productive populations in Brassica campestris var. 'brown sarson'? : Part 3. Potential of component characters in population breeding

Results on 167 f1 'mucromphs' reported earlier were re-examined with the view of determining the potential of component characters in correct identification of parental gca status and F1 heterosis. It was found that a judicious combination of 'plant' and 'ratio' characters would be of direct usefulness in assessing population performance. The role of seedling characters in the process of making a desired level of multiple cross was illustrated. It was found that H X L mucromphs could provide a broad genetic base which has a higher probability of getting channelised into productive populations. It was concluded that 'multiple cross-multiple pollen hybrids' can provide a feasible solution for breeding productive composite populations in Brassica campestris.

Are 'multiple cross-multiple pollen hybrids' an answer for productive populations in Brassica campestris (var.) Brown Sarson? : Part 2: evaluation of 'mucromphs'

A set of 167 'mucromphs' was evaluated in their F1 generation for seven 'plant', four 'plot' and five 'ratio' characters. Methods of characterizing the parents and the hybrids on the basis of combining ability effects described in the first part were found to be efficient in identifying desirable cross combinations for pedigree breeding or generating composite populations. Order effects of multiple-pollen combinations were found to be potent for a number of character components. High x Low cross-combinations were found to produce a high frequency of heterotic crosses followed by High x High. Selected biparental progenies, single crosses, three-way crosses and elite varieties were successful female parents and combinations of pollen from two varieties, one variety and three varieties were successful male parents, in that order, in producing significant heterosis in mucromphs. The relationship between general and specific combining ability on the one hand and realised heterosis on the other was discussed.

Are "multiple cross-multiple pollen hybrids' an answer for productive populations in Brassica campestris var. 'brown sarson'? : I. Methods for studying 'mucromphs'

A set of complex crosses with multiple crosses as female parents were made using multiple pollen in turnip rape (Brassica campestris L.). These multiple cross - multiple pollen hybrids (mucromphs) were evaluated for a large number of quantitative characters including yield. New methods were proposed to study such genetic material in depth so as to formulate suitable strategies to breed for attractive seed yield.

A non-destructive selection criterion for fibre content in jute : III. the criterion and its prospects

A new prediction formula using a geometrical description of the jute plant is proposed and was found to predict the single plant fibre yield to a remarkable degree of accuracy. After an incisive evaluation of 20 component characters, plant height, basal and mid-diameters, basal and mid-sample fibre densities were selected to formulate the non-destructive prediction criterion. Its superiority was upheld when tested in five environments extending over a period of three years, 110 genetically distinct entries and 3080 single plants. The prospects of this criterion in reorienting the existing breeding technology and devising new ones are discussed.

An analysis of association of components of yield and oil in safflower (Carthamus tinctorius L.)

Inter-relationships of various component characters with yield and oil content were analysed using 215 entries of safflower from India and U.S.A. Correlation of capsule number per plant and capsule weight with yield per plant was pronounced and they showed large direct effects on yield. All other components influenced seed yield mainly through these two components. Seed size had little effect on yield while seed number exerted a positive influence. The proportion of hull expressed as per cent of the whole seed revealed a highly significant and inverse relationship with oil content and was mainly responsible for the observed variability in oil content in the material. Although negative association was indicated between seed size and oil content, it was observed to be due to the indirect effect of hull content and not due to direct effect of seed size. Interestingly, yield per plant and its major components, number of capsules and capsule weight, revealed a negligible relationship with oil content. Both direct as well as indirect effects of hull percent and yield per plant were responsible for the favourable effect of seed number on oil content. The correlation of plant height, days to first flowering and total crop growth period with yield and oil content was either negligible or low, offering scope for developing early maturing and dwarf varieties with high yield and oil content. Spine index showed a non-significant association with yield and oil content. Capsule number, capsule weight and hull per cent were observed to be the most important components in breeding for higher yield and oil content.

The utility of covariance of combining ability in plant breeding

The definition of covariances of half- and full sibs, and hence that of variances of general and specific combining ability with regard to a quantitative character, is extended to take into account the respective covariances between a pair of characters. The interpretation of the dispersion and correlation matrices of general and specific combining ability is discussed by considering a set of single, three- and four-way crosses, made using diallel and line × tester mating systems in Pennisetum typhoides. The general implications of the concept of covariance of combining ability in plant breeding are discussed.

A quantitative evaluation of inter-varietal hybrids of Brassica campestris L

A quantitative evaluation of yield components was carried out in 150 inter-varietal hybrids of Brassica campestris using five each of the three varieties, brown sarson (BS) , yellow sarson (YS) and toria (TR). The results showed both additive and non-additive gene action for plant height, number of primary and secondary branches and number of siliquae on the main axis in all the six cross combinations BS-YS, YS-BS, BS-TR, TR-BS, YS-TR and TR-YS. The general combining abilities of BS, YS and TR indicated that their nature and magnitude depended largely on the other parents which entered the hybrids. There were differences in combining ability between direct and reciprocal combinations. GBS II, Kanpur Lotni 17, Kanpur Lotni 27 and DS 17D in BS, IB 3, IB 5, IB 6 and BP 12 in YS , and T 165, T 244 and T 1842 in TR were identified as potential parents for inter-varietal hybridisation. Reciprocal effects were found when BS or YS was used as parent and they were least when TR was used as a parent. The amount and degree of heterosis was substantial in inter-varietal crosses. Based on the heterosis-combining ability relationship, the role of inter-varietal hybridisation in population improvement of Brassica campestris is discussed. A number of methods of utilising the inter-varietal hybrids in multiple crosses and synthetic complexes is suggested as potential supplements to population breeding in this crop.

A non-destructive selection criterion for fibre content in jute : II. Regression approach

An experiment with ten populations of jute, comprising varieties and mutants of the two species Corchorus olitorius and C.capsularis was conducted at two different locations with the object of evolving an effective criterion for selecting superior single plants for fibre yield. At Delhi, variation existed only between varieties as a group and mutants as a group, while at Pusa variation also existed among the mutant populations of C. capsularis.A multiple regression approach was used to find the optimum combination of characters for prediction of fibre yield. A process of successive elimination of characters based on the coefficient of determination provided by individual regression equations was employed to arrive at the optimal set of characters for predicting fibre yield. It was found that plant height, basal and mid-diameters and basal and mid-dry fibre weights would provide such an optimal set.

A Study on the nature of genetic divergence in rice from assam and North East Himalayas

A representative group of 190 rice types collected from North-East India along with four standard varieties, three of which were indicas and one japonica, was studied to understand the nature of genetic divergence. Preliminary grouping was done by canonical analysis and the resultant 42 groups were further classified using the D(2) statistic.The final grouping resulted in nine divergent clusters. The three indica standards were found in three different clusters indicating the wide available variability among them. The japonica standard formed a separate group by itself. A majority of the North-East Indian types formed clusters with indicas, whereas some were intermediate and still others were closer to japonica or indica, thus indicating a series of intergrades bridging indica and japonica.Height followed by leaf area was found to be important for primary and 100-grain weight, followed by amylose content for secondary differentiation. It appears that natural selection as well as human selection might have operated for characters differentiating rice types in Assam and North Eastern Himalayas. Geographical distance was not found to be related to genetic divergence. The study suggests that O. sativa contains innumerable but divergent forms, and its classification into definite varietal groups on an arbitrary basis such as isolation barrier, sexual affinity or geographic distribution would be far from reality.