Polyploidy Improves Photosynthesis Regulation within the Ranunculus auricomus Complex (Ranunculaceae)

Polyploidy has substantially contributed to successful plant evolution, and is often connected to a higher resilience to environmental stress. We test the hypothesis that polyploids tolerate light stress better than diploids. The Ranunculus auricomus complex comprises diploid (2x), tetraploid (4x), and hexaploid (6x) cytotypes, the former of which occur in shaded habitats and the latter more in open, sun-exposed habitats in Central Europe. In this study, we experimentally explored the effects of ploidy and photoperiod extension on the efficiency of photosystem II in the three cytotypes in climate growth chambers. Quantum yields and various coefficients that can be calculated from light curve, Kautsky curve, and fluorescent transient OJIP experiments provided support for the hypothesis that, in comparison to diploids, the improved regulation of excess light by more efficient photochemical and non-chemical quenching in polyploids might have facilitated the adaptation to unshaded habitats. We suggest how lower stress levels in reproductive tissues of polyploids might have favored asexual reproduction.

Chlorophyll Fluorescence - a Tool for Quick Identification of Accase and ALS Inhibitor Herbicides Performance

ABSTRACT: Chlorophyll fluorescence measurement is a precise research technique that can be used for studying the effect of herbicides with different modes of action on photosynthetic apparatus. The aim of the present project was to study the variation of the fluorescence induction curve (Kautsky curve) and its variables affected by pinoxaden (ACCase inhibitor) and mesosulfuron-methyl + iodosulfuron herbicide (ALS inhibitor) in littleseed canarygrass (Phalaris minor Retz.) and wild oat (Avena ludoviciana Durieu). This study was carried out at the Greenhouse of Collage of Agriculture at Ferdowsi University of Mashhad, during 2013. Experiments were performed based on a completely randomized design in form of a dose-response test with six doses of each herbicide plus an untreated control. The maximum quantum efficiency of photosystem II (PSII) was measured 1, 2, 3, 5 and 7 days after spraying (DAS). The results obtained in the study indicated that the estimated EDs parameters differed based on herbicide types or weed species. For example, ED90 varied from 11.67 to 28.61 g active ingredient (a.i.) ha-1. Moreover, the results showed that application of mesosulfuron-methyl + iodosulfuron at doses higher than 9 g a.i. ha-1 changed the shape of the chlorophyll fluorescence induction curve (Kautsky curve) in littleseed canarygrass at 7 DAS while herbicide doses of mesosulfuron-methyl + iodosulfuron did not change the shape of the Kautsky curve in wild oat. In addition, the Kautsky curve was observed to have an approximate permanent drop for littleseed canarygrass species at 2 DAS by pinoxaden. Comparing the fluorescence parameters in wild oat and littleseed canarygrass treated with two herbicides showed that Fv/Fm, the maximum quantum efficiency of PSII and Fvj, variable fluorescence at the J step of littleseed canarygrass decreased more than the mentioned parameters in wild oat. Furthermore, there was a strong relationship ranging from 0.53 to 0.79 between dry weights after 4 weeks and fluorescence parameters at 7 DAS depending on the herbicide type and weed species. Applying fluorescence parameters a few days after treatment to predict biomass production can be a defining criterion in research and development stages of herbicides to eliminate the need for whole plant bioassay. This method can also be applied to shorten the bioassay screening period and function as a suitable and cost effective indicator for monitoring of ACCase and ALS inhibitors. This approach also demonstrates serious damages to plant photosynthesis apparatus on crop during herbicide misapplication.

The Effect of Sugar Beet Broadleaf Herbicides on Fluorescence Induction Curves in Amaranthus retroflexus L. and Portulaca oleracea L.

Chlorophyll fluorescence analysis is a simple and rapid method for detecting herbicide effects after a short time following their application in photosynthetic apparatus in plants. Chlorophyll fluorescence measurements were carried out against two broad of weeds to describe how the Kautsky curve and its parameters were affected by herbicides. Desmedipham + phenmedipham + ethofumesate changed the chlorophyll fluorescence induction curve at all time intervals except four hours after spring (HAS) in Amaranthus retroflexus L. and at all doses of Portulaca oleracea L. 4 HAS. In contrast, chlorophyll fluorescence inhibition was evident by chloridazon at doses of 650 and 325 g a.i. ha-1 in P. oleracea and A. retroflexus respectively, for all time intervals. Furthermore, chlorophyll fluorescence decays only occurred by clopyralid in A. retroflexus at the highest dose. A biomass effective dose (ED50 and/or ED90) based on log-logistic dose-response curves for A. retroflexus were considerably higher than that of P. oleracea. The maximum quantum efficiency (FV/Fm) was stable, whereas the relative changes at the J step (Fvj) and area (the area between the Kautsky curve and the maximum fluorescence (Fm)) was more sensitive to all three herbicides. There was a relatively good correlation between fluorescence parameters taken 24 hours after the spraying and the dry matter taken three weeks later, for both species under study.

Behavior of Sethoxydim Alone or in Combination with Turnip Oils on Chlorophyll Fluorescence Parameter

Sethoxydim is an acetyl-coenzyme A carboxylase (ACCase) inhibitor that changed the shape of the chlorophyll fluorescence curve (kautsky curve) in wild oat (Avena ludoviciana Durieu.) in greenhouse experiment. This experiment was conducted as completely randomized factorial design with three replications at the College of Agriculture, Ferdowsi University of Mashhad, Iran, during 2012. Results of this study revealed that sethoxydim only and plus emulsifiable turnip oil changed the shape of the chlorophyll fluorescence curve (kautsky curve) 7 days after spraying. Sethoxydim plus emulsifiable turnip oil changed the shape of the kautsky curve more than for sethoxydim only. We found that in our study the fv/fm (maximum quantum efficiency) was closely linked to the fresh and dry weight dose-response. Sethoxydim plus emulsifiable turnip oil proved more rapidly effect on fv/fm in comparison with sethoxydim only. The fresh and dry weight dose-response relationship with fv/fm showed a similar behavior. This study revealed a good relation between fresh and dry weight according with values of 28 DAS and fv/fm 7 DAS. In general, the findings of this study revealed that Fv/Fm is a good parameter for evaluating effect of sethoxydim little time after spraying. Also, this research showed that 4 folds more time for classical screening methods comparing to chlorophyll fluorescence method. Thereupon, classical screening methods may be replaced by chlorophyll fluorescence method in future.

Key differences in photosynthetic characteristics of nine species of intertidal macroalgae are related to their position on the shore

A study of the fluorescence characteristics, net photosynthetic rate, and dark respiration of nine species of intertidal macroalgae, from three divisions and from different positions on a rocky shore on the east coast of Scotland, was carried out to address the following questions: (i) Do algae at different positions along the shore respond differently to the stresses at these positions in terms of photosynthetic efficiency, net photosynthetic rate, and respiration, when fully hydrated? (ii) Do algal species at different positions respond differently, in terms of function, to desiccation, and can these responses be correlated with tolerance or intolerance to desiccation in terms of recovery? The present study demonstrated that algal species that occur higher on the shore have greater photosynthetic rates, respiration rates, maximum fluorescence / initial fluorescence ratios, and photosynthetic efficiencies while fully hydrated than do species that live lower on the shore. These findings point towards an increase in time-use efficiency in species that have less time available for productivity or nutrient uptake, since species at a greater height on the shore spend less time in a state of sufficient hydration to photosynthesize. Furthermore, algae higher up the shore, which can recover from desiccation, have significantly different fluorescence characteristics from nonrecoverers, particularly in the area above the Kautsky curve between initial fluorescence and maximum fluorescence. This is the first biophysical evidence relating to a mechanism for desiccation tolerance in macroalgae, and it is discussed within the context of other examples of increasing rates of physiological processes with decreasing time.Key words: fluorescence, zonation, function, rocky shore, Fucus.