Interestingly, the constitutive over-accumulation and exogenous application of hormones may exhibit entirely different effects on the photosynthetic machinery. For instance, the constitutive expression of the gene showed negative effects on the biosynthesis of auxins and GAs that in turn hindered plant growth and development . However, the exogenous application of ABA reduced the heat-induced PSII damage and induced thermostability in barley seedlings . These findings suggest that plants producing more endogenous levels of ABA should be more tolerant to environmental stresses compared to control plants. This also reflects the large number of reports where hormonal metabolic pathways have been altered through genetic engineering to induce inherent abiotic stress tolerance in plants. At the same time, studies focusing on the influence of the exogenous application of hormones remain equally relevant; however, it is speculated that transcriptomics and proteomic analyses of plants’ responses to various hormones in mutants with altered photosynthesis could provide more details that would eventually facilitate crop-improvement programs. Furthermore, more efforts are warranted to elucidate the physiological relevance of altered expression reported in many abiotic stress-responsive genes, genes, and genes that encode intrinsic and extrinsic proteins of the PSII complex. In addition, metabolomic approaches are expected to play a significant role in understanding the influence of hormones on the metabolic responses of plants for the acclimation of the photosynthetic apparatus under environmental stress. A combination of datasets from different approaches would certainly enhance our knowledge of the physiological significance of phytohormones in photosynthetic efficiency under various environmental stress conditions.
Beside studies on mutant plants, the exogenous application of BRs has been studied extensively in various crops under normal and abiotic stress conditions (). BRs alleviated Cd-induced metal toxicity on the primary photochemistry of PSII in rape cotyledons by maintaining efficient ETC and limiting the damage in OEC and PSII reaction centers . Several other reports are documented where BR was shown to mitigate the loss of chlorophyll molecules and the reduction in carbonic anhydrase activity in various crops exposed to Cd- or aluminum-induced metal toxicity [,,,].
The photosynthesis efficiency of a healthy plant can reach up to 83%. When a plant is under stressful conditions photosynthesis decreases, sometimes even to the point that no light is absorbed at all. The amount of stress is determined by measuring the plants fluorescence. Under normal conditions, when photosynthesis efficiency is high, fluorescent emission is low. However, when a plant is under stressful conditions photosynthesis efficiency is low, and fluorescent emission is high. The experiments carried out in these case studies measure the plant’s stress level when put under potentially damaging conditions.
New foliage wilting in the heat of the day is a symptom of inadequate water. It is a natural reaction under these conditions of extreme stress. Flowers on a dry plant will sometimes start to open and then fall off without opening, as shown in the photo below. In hot weather, the wilting occurs naturally in the heat of the day. If should go away by the next morning. If it doesn't, the ground is probably dry. However, since the same condition can be caused by root fungi which thrive in warm moist conditions, it is important not to over-water. If the soil is truly dry, then a deep watering in needed. Sandy soils require more irrigation. The soil should not remain wet. Make sure the soil is getting dry before watering. Leaf wilt due to root rot is caused by too much water, so first instincts may be wrong. Check the soil before watering. [Photo courtesy of Harold Greer] [
Phytophthora Dieback, The oomycete, or water mold, Phytophthora causes one of the most common disease problems in the landscape for rhododendrons and azaleas. This oomycete is a "water mold," and thrives in poorly drained or wet conditions. A wilted plant is usually the first sign of trouble. Rhododendron leaves will curl inward and droop. Drought can cause similar symptoms. Roots of affected plants appear soggy or blackened, and the outer portion of the root easily pulls away from the inner portion. Crown rot causes the lower portions of the stem to have a brown discoloration of the wood near the soil line. This disease is favored in poorly drained areas or when plants are set too deeply. Plants may remain without symptoms until further stressed from drought or flooding. Azaleas. Resistant: R. sanctum, R. simsii (Indian azalea), R. yedoense var. poukhanense (Korean azalea), 'Corrine,' 'Fakir,' 'Fred Cochran,' 'Glacier,' 'Hampton Beauty,' 'Higasa,' 'Merlin,' 'Polar Sea,' 'Rose Greeley'. Moderately resistant: 'Alaska,' 'Chimes,' 'Eikan,' 'Jan Cochran,' 'Morning Glow,' 'New White,' 'Pink Gumpo,' 'Pink Supreme,' 'Rachel Cunningham,' 'Red Wing,' 'Shinkigen,' 'Sweetheart Supreme'. Rhododendrons. Resistant: 'Caroline,' 'Martha Isaacson,' 'Pink Trumpet,' 'Prof. Hugo de Vries,' 'Red Head,' R. davidsonianum, R. delavayi, R. glomerulatum, R. hyperythrum, R. lapponicum, R. occidentale, R. poukhanense, R. pseudochrysanthum, R. quinquefolium and R. websterianum. Do not set new plants any deeper than the original soil level. Ensure the root collar is exposed and free of soil and mulch. Rhododendrons and azaleas are subject to collar rot when root flares are buried. When planting in poorly drained soils create raised beds or provide sub-surface drainage. Plant with the root collar exposed. If soil is compacted, prepare planting area by cultivating and incorporating organic matter. Firm the soil slightly at the base of the planting hole to prevent the plant from settling into the bed. Also, keep the mulch back 2 to 3 inches from the stem. Do not plant azalea and rhododendron plants into sites where plants have previously died from root rot. Even resistant plants may succumb under these conditions. The oomycete survives in the soil and cannot be eradicated once an area is infected. Also see , and .
Under these conditions C4 photosynthesis has developed a number of times in a number of plant lines in the 25-30 million years since the late Oligocene, getting to todays numbers by the end of the Miocene.Assuming that low CO is a pre-condition for the development of C4 plants, paramaters such as increasing aridity, high light habitats, increasing temperature and seasonality, fire, and the distribution of grazing animals, are all thought to play an important part in this evolutionary trend.At temperatures 22C - 30C, Quantum yields for C3 and C4 plants are the same
Temperatures above 30C, quantum yields are greater in C4 plants
Temperatures below 22C, quantum yields are greater in C3 plants.
Very few plants stay pest-free forever. Pest insects are more likely to be encountered on indoorplants than diseases because the interior environment rarely offers favorable conditions for foliardiseases to develop. However, when plants are grown under stressful conditions (such as lowlight and excess water), soil-borne pathogens often develop.
The central theme of the present book is to unravel the mechanisms of photosynthesis under optimal and stressful environments and gain insight into the processes which can lead to a better understanding of the photosynthetic inhibition due to various constraints and provide measures to improve photosynthetic mechanisms under these conditions.
Scientists have an increasingly sophisticated understanding of mechanisms that ensure efficient photosynthesis under laboratory-controlled light conditions. But less is known about the regulation of photosynthesis when plants experience rapid and extreme changes in sunlight, which can potentially cause harmful effects on photosynthetic efficiency and productivity.
Rao, and Juan Andres Cardoso PHOTOSYNTHESIS UNDER ENVIRONMENTAL STRESS CONDITIONS Photosynthesis in Plants under Stressful Conditions Rama Shanker Dubey Effects of Salinity and Drought Stress on Photosynthesis, Growth, and Development of Ornamental Plants Hyun-Sug Choi, Xiaoya Cai, and Mengmeng Gu Photosynthetic Strategies of Desiccation-Tolerant Organisms Beatriz Fernandez-Marin, Andreas Holzinger, and Jose Ignacio Garcia-Plazaola Drought Tolerance of Photosynthesis Katya Georgieva and Gergana Mihailova Photosynthesis under Heat Stress Muhammad Farooq, Abdul Rehman, Abdul Wahid, and Kadambot H.M.
It details all photosynthetic factors and processes under normal and stressful conditions, explores the relationship between photosynthesis and other plant physiological processes, and relates photosynthesis to plant production and crop yields.
Any change in the surrounding environment may disrupt homeostasis. Environmental modulation of homeostasis may be defined as . Thus, it follows that implies some adverse effect on the physiology of a plant induced upon a sudden transition from some optimal environmental condition where homeostasis is maintained to some suboptimal condition which disrupts this initial homeostatic state. Thus, plant stress is a relative term since the experimental design to assess the impact of a stress always involves the measurement of a physiological phenomenon in a plant species under a suboptimal, stress condition compared to the measurement of the same physiological phenomenon in the same plant species under optimal conditions.