Low photosynthetic activity is linked to changes in the organization of photosystem II in the fruit of Arum italicum

Photosynthesis in non-foliar tissues: implications for yield

Photosynthesis is currently a focus for crop improvement. The majority of this work has taken place and been assessed in leaves, and limited consideration has been given to the contribution that other green tissues make to whole-plant carbon assimilation. The major focus of this review is to evaluate the impact of non-foliar photosynthesis on carbon-use efficiency and total assimilation. Here we appraise and summarize past and current literature on the substantial contribution of different photosynthetically active organs and tissues to productivity in a variety of different plant types, with an emphasis on fruit and cereal crops. Previous studies provide evidence that non-leaf photosynthesis could be an unexploited potential target for crop improvement. We also briefly examine the role of stomata in non-foliar tissues, gas exchange, maintenance of optimal temperatures and thus photosynthesis. In the final section, we discuss possible opportunities to manipulate these processes and provide evidence that Triticum aestivum (wheat) plants genetically manipulated to increase leaf photosynthesis also displayed higher rates of ear assimilation, which translated to increased grain yield. By understanding these processes, we can start to provide insights into manipulating non-foliar photosynthesis and stomatal behaviour to identify novel targets for exploitation in continuing breeding programmes.

Frequently asked questions about chlorophyll fluorescence, the sequel

Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122:121-158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additional Chl a fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of F V /F M values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl a fluorescence in biosensor applications and the application of neural network approaches for the analysis of fluorescence measurements. The answers draw on knowledge from different Chl a fluorescence analysis domains, yielding in several cases new insights.

Cyto-histological and morpho-physiological responses of common duckweed (Lemna minor L.) to chromium

Along with cadmium, lead, mercury and other heavy metals, chromium is an important environmental pollutant, mainly concentrated in areas of intense anthropogenic pressure. The effect of potassium dichromate on Lemna minor populations was tested using the growth inhibition test. Cyto-histological and physiological analyses were also conducted to aid in understanding the strategies used by plants during exposure to chromium. Treatment with potassium dichromate caused a reduction in growth rate and frond size in all treated plants and especially at the highest concentrations. At these concentrations the photosynthetic pathway was also altered as shown by the decrease of maximum quantum yield of photosystem II and the chlorophyll b content and by the chloroplast ultrastructural modifications. Starch storage was also investigated by microscopic observations. It was the highest at the high concentrations of the pollutant. The data suggested a correlation between starch storage and reduced growth; there was greater inhibition of plant growth than inhibition of photosynthesis, resulting in a surplus of carbohydrates that may be stored as starch. The investigation helps to understand the mechanism related to heavy metal tolerance of Lemna minor and supplies information about the behavior of this species widely used as a biomarker.

The non-foliar hypoxic photosynthetic syndrome: evidence for enhanced pools and functionality of xanthophyll cycle components and active cyclic electron flow in fruit chlorenchyma

Green fruits display a high engagement in CEF and enhanced VAZ cycle activity as a response to the demands imposed by their internal aerial conditions, particularly low O 2 , due to gas exchange limitations. In the present study, we used HPLC analysis, post-illumination changes in fluorescence yield under varying O2 and CO2 partial pressures and absorbance changes at 820 nm induced by far-red light to assess the carotenoid composition, the functionality of the xanthophyll cycle (VAZ) and the possibility of an active cyclic e (-) flow (CEF) in the fully exposed green fruits from Nerium oleander and Rosa sp. Equally exposed, mature leaves served as controls. Compared to leaves, fruits display less total chlorophylls and carotenoids but higher Car/Chl ratio, mainly shaped by the increased pools of the VAZ cycle components, in both species. The enhanced VAZ pool size in fruits is combined with a higher mid-day de-epoxidation state (DEPS). Moreover, fruits exhibit considerably lower levels of oxidizable P700, a faster re-reduction of PSI and significantly higher relative magnitude of CEF, irrespective of the O2/CO2 levels applied. We conclude that the higher VAZ investment may serve the enhanced heat dissipation needs in fruits, in the presence of a suppressed linear e (-) flow. In addition, the elevated potential of CEF may replenish the ATP lost due to hypoxia and concurrently facilitate the development of adequate non-photochemical quenching (NPQ), through its contribution to ΔpH increase. Since other non-foliar green organs exhibit a similar photosynthetic pattern, we argue that this may reflect a common strategy for green tissues under similar micro-environmental conditions, particularly hypoxia.

Frequently asked questions about in vivo chlorophyll fluorescence: practical issues

The aim of this educational review is to provide practical information on the hardware, methodology, and the hands on application of chlorophyll (Chl) a fluorescence technology. We present the paper in a question and answer format like frequently asked questions. Although nearly all information on the application of Chl a fluorescence can be found in the literature, it is not always easily accessible. This paper is primarily aimed at scientists who have some experience with the application of Chl a fluorescence but are still in the process of discovering what it all means and how it can be used. Topics discussed are (among other things) the kind of information that can be obtained using different fluorescence techniques, the interpretation of Chl a fluorescence signals, specific applications of these techniques, and practical advice on different subjects, such as on the length of dark adaptation before measurement of the Chl a fluorescence transient. The paper also provides the physiological background for some of the applied procedures. It also serves as a source of reference for experienced scientists.

Comparison of photosynthesis recovery dynamics in floating leaves of Trapa natans after inhibition by manganese or molybdenum: effects on Photosystem II

The aquatic plant Trapa natans L. is highly resistant to Mn and moderately resistant to Mo, mainly thanks to its ability to sequestrate the metals by chelation in the vacuole. Excess of Mn and Mo causes somewhat aspecific toxicity symptoms in plants, but the main target of their toxicity seems to be the photosynthetic process. In this work, we aimed at understanding how the effect on photosynthesis caused by Mn (130 μM, full recovery) or Mo (50 μM, partial recovery) in T. natans is linked to changes occurring in the photosynthetic apparatus, with emphasis on Photosystem II (PSII), during a 10 day treatment with these metals. The time-course of net photosynthesis, photosynthetic pigment content, amount of PSII and its peripheral antenna LHCII, and room-temperature fluorescence emission ratios F694/F680 and F700/(F685 + F695) showed that the early inhibiting effect of Mo and Mn (one day exposure) was essentially non-specific with respect to the metal, though more marked in Mo- than in Mn-treated plants. During the subsequent recovery phase, Mo still impaired PSII assembly and, consequently, photosynthesis could not reach the control values. Conversely, in Mn-treated plants the amount of PSII was fully re-established, as was photosynthesis, but the metal induced the accumulation of LHCII. The extent of inhibition and the effectiveness of photosynthesis recovery are proposed to reflect the different ability of T. natans to sequestrate safely excess Mn or Mo in vacuoles.