The intensity of and recovery from photoinhibition under drought in a thermotolerant common bean compared to drought tolerant genotypes

Abstract

The chlorophyll a fluorescence parameters of four Phaseolus vulgaris L. genotypes were evaluated under drought in two greenhouse experiments. Under severe water stress, the thermotolerant genotype 'Diplomata' maintained significantly higher values of predawn leaf water potential (Ψw), maximum Fv/Fm and effective (ΦPSII) quantum yield of photosystem II , and non-photochemical quenching than 'Ouro Negro', in the first experiment, and 'A 285' and 'A 222', in the second one. Among these parameters, Fv/Fm showed more differences that discriminated between the genotype responses even when measured at night. Next, a difference between Fv/Fm after sundown and Fv/Fm at dawn on the same day (day ∆Fv/Fm), i.e., the intensity of photoinhibition, and a difference between Fv/Fm at dawn and Fv/Fm after sundown on the day before (night ∆Fv/Fm), i.e. the photoinhibition recovery, were evaluated. Day ∆Fv/Fm and night ∆Fv/Fm were significantly higher for 'Diplomata' under severe water stress in both experiments. In addition, 'Ouro Negro' in the first experiment and all the genotypes in the second showed negative values of night ∆Fv/Fm on the last day of drought when their Ψw were also minimal indicating no recovery from photoinhibition and the need for rehydration. At maturation, stressed plants of 'Diplomata' showed a significantly higher yield than 'Ouro Negro' in the first experiment and the same as 'A 285' in the second. Therefore, the thermotolerant genotype 'Diplomata' also showed drought tolerance, and the use of day ∆Fv/Fm and night ∆Fv/Fm fluorescence analysis was able to discriminate between the tolerances of these genotypes and to indicate the need for rehydration.

A New Application of Fluorescence Measurements to Discriminate the Behavior of Plants under Environmental Stress

“…A decrease in these values is related to the closure of the reaction centers and the processes of energy extinction in the form of heat [2]. According to Zlatev (2009) [5], when observing the behavior of wheat plants under drought, he concluded that photoinhibitory damage to PSII may be a secondary effect of drought [6]. This same study revealed that the Katia wheat variety showed greater tolerance to drought regarding photosynthetic activity since the Fv/Fm parameter remained high during the drought.…”

“…Then, the difference between Fv/Fm after sunset minus Fv/Fm at dawn of the same day (day ∆Fv/Fm) and the difference between Fv/Fm at dawn minus Fv/Fm after sunset on the previous day (night ∆Fv/Fm) were evaluated [6]. The day ∆Fv/Fm was used to assess the effect of the photoinhibition during the day, and the night ∆Fv/Fm showed the capacity of recovery from the photoinhibition of the day before.…”

Plant Responses to Water Deficit and Photo Inhibition

“…In the field, drought is generally associated with a high PPFD due to a clear sky, and photoinhibition an oxidative stress will occur even under moderate water stress, as shown in (Figure 1) [5]. Water deficit affects several physiological responses, varying in intensity among the species, its growth stages, and cultivation conditions [6].…”

“…There is a reduction in A under mild water deficiency, but the causes of this reduction are still under debate. Some authors state that there is only a limitation of CO 2 substrate, a diffusional limitation due to stomatal closure under mild stress [5]. Nevertheless, at the onset of drought, there is stomata closure and a reduction of cell growth and protein synthesis and thus carbohydrate synthesis [6].…”

“…For example, the non-photochemical quenching (NPQ) values, i.e., energy dissipation to avoid photoinhibition, were almost double in the second experiment compared with the first. The high NPQ indicated a higher energy dissipation, primarily by heat [2,3], to avoid more intense photoinhibition in the second experiment [5]. Therefore, a metabolic effect of water deficit on A, due to oxidative stress under high PPFD, as occurs in nature during drought, is evident (Figure 3), showing a diffusional and metabolic effect even during the onset of drought.…”