Chlorophyll Fluorescence

... Michael E. Loik a , ¶ , Travis E. Huxman c , b , Erik P. Hamerlynck d , b and Stanley D. Smith b. ... 19. ME Loik, CD St. Onge and J. Rodgers, Post-fire recruitment of Yucca brevifolia and Yucca schidigera in Joshua Tree National Park, California. ...

Vetiver grass (Vetiveria zizanioides) has been widely confirmed to have very strong tolerance to flooding and even complete submergence and, therefore, is a considerably excellent species for stabilization and revegetation of "wet" barren slopes and for wastewater treatment. However, it is poorly documented why vetiver is so tolerant to submergence. To understand the mechanisms of vetiver's tolerance to submergence, an

The effects of water deficit on photochemical parameters and activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as, cellular damages were investigated in two clones of Coffea canephora differing in drought tolerance. After 6 days without irrigation, predawn leaf water potential fell to −3.0 MPa that was accompanied by the suppression of net photosynthesis in both clones. The variable to maximum chlorophyll fluorescence ratio remained unchanged regardless of the imposed treatments. Both clones showed a similar decline (about 25%) in the photochemical quenching coefficient, but only the drought-sensitive clone exhibited an enhancement (31%) of thermal deactivation under water deficit conditions. The quantum yield of electron transport decreased similarly in both genotypes. Under drought conditions, activities of SOD, CAT and APX increased to a greater extent in the drought-tolerant clone than in the drought-sensitive one. This seemed to be matched with higher protection against oxidative stress, as judged from the lower levels of lipid peroxidation and electrolyte leakage in the drought-tolerant clone. Thus, the ability to increase the antioxidant system activity in order to limit cellular damages might be an important attribute linked to the drought tolerance in C. canephora.

Coffee is the most traded commodity in the world, and Brazil is its largest producer. Coffee leaf rust, caused by the biotrophic fungus Hemileia vastatrix, is the most important coffee disease, reducing coffee yield by 35–50%. This study aimed to use the ratio of variable and maximum fluorescence of dark-adapted tissue (Fv/Fm) as a parameter to differentiate presymptomatic tissue from healthy tissue during disease development in plants sprayed with pyraclostrobin and epoxiconazole after 4 days postin- oculation. Visual severity was considered as an indicative of apparent dis- ease and true severity as an indicative of both apparent and non-apparent disease. There was a significant linear relationship between the areas of true severity and visual severity, and for each additional unit in the visual severity, there was an increase of 1.53 units on the true severity. For the epoxiconazole and pyraclostrobin treatments, coffee leaf rust symptoms decreased according to both visual and Fv/Fm images. Pustules on the leaves sprayed with epoxiconazole were smaller in size than those on the leaves of non-sprayed plants but bigger than those sprayed with pyraclost- robin. The reduction in Fv/Fm values at the pustule epicentres present on the leaves of plants sprayed with epoxiconazole, and pyraclostrobin was greater than those of the non-sprayed plants. This finding was expected and reflects the importance of these fungicides in prohibiting the progress of coffee leaf rust. The photosynthetic capacity of Coffea arabica was affected by H. vastatrix infection, and the Fv/Fm parameter was able to show this effect before the visual symptoms were noticed.

The analysis was based on the results of field experiment carried out in 2013-2015 in Parczew (51°38′N, 22°54′E), using the method of randomized subblocks in 3 replications. The research factor were herbicides: A – Dispersive Afalon 450 SC 450 S.C. – 1.5 dm ha-1; B) Dispersive Afalon 450 SC + Command 480 SC (1 dm + 0.2 dm ha-1); C – Racer 250 SC – 1.5 dm ha-1; D) Sencor 70 WG + Racer 250 SC (0.5 kg + 1.0 dm ha-1); E) control object with mechanical care. The research object was the Polish Albik cultivar. Mineral (100 kg N, 100 kg P2O5, 150 kg K2O.ha-1) and organic (25 t ha-1) fertilization was constant. Tubers were planted with a spacing of 67.5 x 40 cm. Herbicides were applied just before plant emergence and no further treatments were applied later. The degree of phytotoxic effect of the preparation was assessed according to the scale of EWRS. Photosynthetic activity of Jerusalem artichoke leaves was determined using a PAM-2000 fluorimeter by Walz GmbH. The following parameters were measured: Fv / Fm – maximum quantum yield of chlorophyll, Y – indicator determining the total quantum gain of photosynthesis and photochemical (Qp) and non-photochemical (Qn) fluorescence quenching coefficients. The content of chlorophyll an and b in fresh leaf mass was determined by the spectrophotometric Arnon method. Phytotoxic damage to Jerusalem artichoke plants caused by the use of the mixture of herbicides Afalon + Command through a temporary inhibition of plant growth negatively affected on the maximum efficiency of PS II photosystems in the dark; PS II performance on light, the current number of electrons in PSII under conditions of adaptation to light, value of photochemical coefficient and non-photochemical quenching of chlorophyll fluorescence. The highest decrease in the content of chlorophyll a was found in the leaves of plants, where the mixture of herbicides Afalon + Command was applied. Dyspersive Afalon 450 SC is a recommendable agricultural practice herbicide for pre-emergence weed control in the cultivation of Jerusalem artichoke, due to the values of chlorophyll fluorescence indicators.

High temperature represents one of the most serious abiotic stress factors limiting plant photosynthesis, biomass production and crop productivity. Photosynthetic apparatus is an important heat sensor in plants, sensing a wide range of air temperatures, from moderate to extreme. In this chapter we offer current knowledge on both photochemical and metabolic changes occurring within the photosynthetic apparatus in conditions of heat stress associated with signaling and stress response. The heat stress directly affects the heat sensitive sites, mainly Oxygen Evolving Complex of Photosystem II and Rubisco activase. It leads to subsequent indirect effects, such as changes of the redox status of individual components on thylakoid membrane in chloroplast and increase in production of Reactive Oxygen Species (ROS). Hence, the redox signaling plays the crucial role in enhancement of alternative electron pathways such as cyclic electron flow as well as triggering the signal transduction pathways resulting to heat stress response. The redox signaling in chloroplast is closely associated with ROS signaling, which interferes with regulation also out of chloroplast. The stress response involves mainly production of specific proteins (mostly heat shock proteins or antioxidants) or protective compounds (osmoprotectants) leading to increase of thermostability of sensitive sites or protection against ROS. Different signal molecules contribute in photosynthesis-related heat-stress signaling pathways, such as reactive oxygen species with hydrogen peroxide, nitric oxide, calcium, abscisic acid, etc. The specific roles of cytokinins and isoprene in heat stress response are also reviewed.