Local weak light induces the improvement of photosynthesis in adjacent illuminated leaves in maize seedlings

Improved photosynthetic performance under unilateral weak light conditions in a wide-narrow-row intercropping system is associated with altered sugar transport

Intercropping improves resource utilization. Under wide-narrow-row maize (Zea mays) intercropping, maize plants are subjected to weak unilateral illumination and exhibit high photosynthetic performance. However, the mechanism regulating photosynthesis under unilateral weak light remains unknown. We investigated the relationship between photosynthesis and sugar metabolism in maize under unilateral weak light. Our results showed that the net photosynthetic rate (Pn) of unshaded leaves increased as the level of shade on the other side increased. On the contrary, the concentration of sucrose and starch and the number of starch granules in the unshaded leaves decreased with increased shading due to the transfer of abundant C into the grains. However, sink loss with ear removal reduced the Pn of unshaded leaves. Intense unilateral shade (40% to 20% normal light), but not mild unilateral shade (60% normal light), reduced grain yield (37.6% to 54.4%, respectively). We further found that in unshaded leaves, Agpsl, Bmy, and Mexl-like expression significantly influenced sucrose and starch metabolism, while Sweet13a and Sut1 expression was crucial for sugar export. In shaded leaves, expression of Sps1, Agpsl, and Sweet13c was crucial for sugar metabolism and export. This study confirmed that unshaded leaves transported photosynthates to the ear, leading to a decrease in sugar concentration. The improvement of photosynthetic performance was associated with altered sugar transport. We propose a narrow-row spacing of 40 cm, which provides appropriate unilateral shade and limits yield reduction.

Effects of exogenous Strigolactone on the physiological and ecological characteristics of Pennisetum purpureum Schum. Seedlings under drought stress

BACKGROUND

Drought is one of the main environmental factors limiting plant growth and development. Pennisetum purpureum Schum. was used to explore the mitigation effects of exogenous strigolactone (SL) on drought stress during the seedling stage. The effects of different concentrations (1, 3, 5, and 7 μmol·L^- 1) of SL on the photosynthesis characteristics, growth performance, and endogenous abscisic acid (ABA) of P. purpureum under drought stress were studied.

RESULTS

Exogenous SL could effectively alleviate the inhibitory effect of drought stress on P. purpureum growth. Compared with drought stress, the net photosynthesis rate, stomatal conductance, transpiration rate, and water-use efficiency of the leaves of P. purpureum after SL treatment significantly increased, thereby exerting a significant mitigation effect on the decrease in photosystem II maximum photochemical efficiency and the performance index based on light absorption caused by drought. Moreover, the exogenous application of SL can effectively increase the fresh and dry weight of the leaves and roots and the main-root length. After applying SL for 120 h, the ABA content of P. purpureum decreased significantly. The activity of key enzymes of photosynthesis significantly increased after 48 h of external application of SL to P. purpureum.

CONCLUSIONS

SL treatment can improve the photosynthesis performance of P. purpureum leaves under drought conditions and increase the antioxidant capacity of the leaves, thereby reducing the adverse effects of drought, promoting the growth of P. purpureum, and effectively improving the drought resistance of P. purpureum.

Low Light Stress Increases Chalkiness by Disturbing Starch Synthesis and Grain Filling of Rice

Low light stress increases the chalkiness of rice; however, this effect has not been fully characterized. In this study, we demonstrated that low light resulted in markedly decreased activity of ADP-glucose pyrophosphorylase in the grains and those of sucrose synthase and soluble starch synthase in the early period of grain filling. Furthermore, low light also resulted in decreased activities of granule-bound starch synthase and starch branching enzyme in the late period of grain filling. Therefore, the maximum and mean grain filling rates were reduced but the time to reach the maximum grain filling rates and effective grain filling period were increased by low light. Thus, it significantly decreased the grain weight at the maximum grain filling rate and grain weight and retarded the endosperm growth and development, leading to a loose arrangement of the amyloplasts and an increase in the chalkiness of the rice grains. Compared to the grains at the top panicle part, low light led to a greater decrease in the grain weight at the maximum grain filling rate and time to reach the grain weight at the maximum grain filling rate at the bottom panicle part, which contributed to an increase in chalkiness by increasing the rates of different chalky types at the bottom panicle part. In conclusion, low light disturbed starch synthesis in grains, thereby impeding the grain filling progress and increasing chalkiness, particularly for grains at the bottom panicle part.

Ovary Abortion Induced by Combined Waterlogging and Shading Stress at the Flowering Stage Involves Amino Acids and Flavonoid Metabolism in Maize

Maize (Zea mays L.) crops on the North China Plain are often subject to continuous overcast rain at the flowering stage. This causes waterlogging and shading stresses simultaneously and leads to huge yield losses, but the causes of these yield losses remain largely unknown. To explore the factors contributing to yield loss caused by combined waterlogging and shading stress at the flowering stage, we performed phenotypic, physiological, and quasi-targeted metabolomics analyses of maize plants subjected to waterlogging, shading, and combined waterlogging and shading (WS) treatments. Analyses of phenotypic and physiological indexes showed that, compared with waterlogging or shading alone, WS resulted in lower source strength, more severe inhibition of ovary and silk growth at the ear tip, a reduced number of emerged silks, and a higher rate of ovary abortion. Changes in carbon content and enzyme activity could not explain the ovary abortion in our study. Metabolomic analyses showed that the events occurred in ovaries and silks were closely related to abortion, WS forced the ovary to allocate more resources to the synthesis of amino acids involved in the stress response, inhibited the energy metabolism, glutathione metabolism and methionine salvage pathway, and overaccumulation of H₂O₂. In silks, WS led to lower accumulation levels of specific flavonoid metabolites with antioxidant capacity, and to over accumulation of H₂O₂. Thus, compared with each single stress, WS more seriously disrupted the normal metabolic process, and resulted more serious oxidative stress in ovaries and silks. Amino acids involved in the stress response in ovaries and specific flavonoid metabolites with antioxidant capacity in silks play important roles during ovary abortion. These results identify novel traits for selection in breeding programs and targets for genome editing to increase maize yield under WS stress.

Solar Radiation Effects on Dry Matter Accumulations and Transfer in Maize

Solar radiation is the energy source for crop growth, as well as for the processes of accumulation, distribution, and transfer of photosynthetic products that determine maize yield. Therefore, learning the effects of different solar radiation amounts on maize growth is especially important. The present study focused on the quantitative relationships between solar radiation amounts and dry matter accumulations and transfers in maize. Over two continuous years (2017 and 2018) of field experiments, maize hybrids XY335 and ZD958 were grown at densities of 4.5 × 104 (D1), 7.5 × 104 (D2), 9 × 104 (D3), 10.5 × 104 (D4), and 12 × 104 (D5) plants/ha at Qitai Farm (89°34'E, 44°12'N), Xinjiang, China. Shading levels were 15% (S1), 30% (S2), and 50% (S3) of natural light and no shading (CK). The results showed that the yields of the commonly planted cultivars XY335 and ZD958 at S1, S2, and S3 (increasing shade treatments) were 7.3, 21.2, and 57.6% and 11.7, 31.0, and 61.8% lower than the control yields, respectively. Also, vegetative organ dry matter translocation (DMT) and its contribution to grain increased as shading levels increased under different densities. The dry matter assimilation amount after silking (AADMAS) increased as solar radiation and planting density increased. When solar radiation was <580.9 and 663.6 MJ/m2, for XY335 and ZD958, respectively, the increase in the AADMAS was primarily related to solar radiation amounts; and when solar radiation was higher than those amounts for those hybrids, an increase in the AADMAS was primarily related to planting density. Photosynthate accumulation is a key determinant of maize yield, and the contributions of the vegetative organs to the grain did not compensate for the reduced yield caused by insufficient light. Between the two cultivars, XY335 showed a better resistance to weak light than ZD958 did. To help guarantee a high maize yield under weak light conditions, it is imperative to select cultivars that have great stay-green and photosynthetic efficiency characteristics.