Different effects of dark treatment on pigment composition and photosystem I and II activities in intact cotyledons and primary leaves of Cucurbita pepo (zucchini)

Abstract

Darkness mediates different senescencerelated responses depending on the targeting of dark treatment (whole plants or individual leaves) and the organs that perceive the signal (leaves or cotyledons). In this study, we presented data on the differential effects of 2-day dark treatment on progression of senescence in cotyledons and primary leaves of 14-day-old plants of Cucurbita pepo L. (zucchini). The lack of changes in chlorophyll a, chlorophyll b and carotenoid contents as well as in the PSI activity measured by the far-red induced alterations in the P 700 oxidation levels and the quantum yield of electron transport from Q A -to PSI end acceptors (u R 0 ) indicated higher resistance of cotyledons to the applied dark stress compared to the primary leaves. In contrast to cotyledons, PSI activity in the primary leaves was significantly inhibited. Concerning the activity of PSII analyzed by the changes in the JIPtest parameters (the maximal efficiency of PSII photochemistry, u P 0 ; the performance index, PI ABS ; the efficiency of Q A -reoxidation, w 0 and the effective dissipation per reaction center, DI 0 /RC), no differences were observed between cotyledons and primary leaves, thus suggesting that PSI activity in the true leaves was more susceptible to the applied dark stress. The transfer of the darkened plants to normal light regime resulted in delayed senescence in cotyledons which was in contrast to results on Arabidopsis, thus implying the existence of specific mechanisms of cotyledon senescence in different monocarpic plants.Keywords Dark-induced senescence and recovery Á Cotyledons and primary leaves Á PSII and PSI activity Á JIP-test Abbreviations PSA Photosynthetic apparatus PSI Photosystem I PSII Photosystem II RC PSII reaction center Chl

Local induction of senescence by darkness in Cucurbita pepo (zucchini) cotyledons or the primary leaf induces opposite effects in the adjacent illuminated organ

“…Thus, data have been published confirming the organ-specific differences between cotyledons and differentiated leaves during natural or whole plant dark-induced senescence (La Rocca et al 1996;Weaver and Amasino 2001;Ananieva et al 2004). Consistent with the specificity of the response, our recent results on pigment content, PSI and PSII activities have shown higher resistance of zucchini cotyledons to the applied whole-plant dark stress as compared to the primary leaves (Mishev et al 2009). …”

“…Our recent results on the potential role of darkness to affect senescence progression when applied to individual Cucurbita pepo (zucchini) cotyledons have shown a strong acceleration of senescence when both cotyledons were darkened for 2 days as determined by deterioration of chloroplast ultrastructure in parallel with a decrease in photosynthetic rate, photochemical quantum efficiency of photosystem II (PSII), endogenous levels of CKs and strong inhibition of chloroplast transcription based mainly on the activity of plasted-encoded RNA polymerse (PEP) (Ananieva et al 2008;Mishev et al 2009Mishev et al , 2011. In contrast, when a single cotyledon was individually darkened, senescence was delayed suggesting the inhibitory effect of the illuminated cotyledon on the senescence of the darkened one (Ananieva et al 2008).…”

Leaf senescence induced by EGY1 defection was partially restored by glucose in Arabidopsis thaliana

“…Leaf senescence could be induced by external stresses, such as darkness. Darkness treatment induced uniform and rapid senescence (Chrost et al 2004 ; del Rio et al 2003 ; Mishev et al 2009 ). After 3 days of dark treatment, egy1 mutant leaves were more yellow while the phenotype of WT plants had no obvious changes (Fig.…”

Chlorophyll fluorescence in rice: probing of senescence driven changes of PSII activity on rice varieties differing in grain yield capacity

“…However, as far as Chl fluorescence parameters are concerned, the authors focused mainly on F v /F m and/or effective quantum yield of PSII (φ PSII ) (Lu et al, 2002;Jiang et al, 2002;Rapacz, 2007). Besides, the existing studies on the changes in Chl fluorescence parameters in rice with senescence were conducted on primary leaves or cotyledons (Yordanov et al, 2008;Mishev et al, 2009). Studies conducted on flag leaves of rice are still not available.…”