Comparative Functioning of Photosynthetic Apparatus and Leaf Water Potential in Zygophyllum eurypterum (Boiss & Bushe) During Phenological Phases and Summer Drought

Abstract

Background: In arid regions, seasons are often marked by differences in rainfall, with life-history events,
along with phenological stages. Materials and Methods: Three phenological phases were distinguished as
vegetative phase (VP), flowering phase (FP) and seeding phase (SP). Chlorophyll fluorescence parameters
(Chl. FPs) such as maximum quantum yield of PSII photochemistry (Fv/Fm), photochemical efficiency of
photosystem II (ΦPSII), effective quantum yield (Fv'/Fm'), photochemical dissipation of absorbed energy (qP)
and non-photochemical dissipation of the absorbed energy (NPQ) along with pigment contents and predawn
leaf water potential (ΨL) were determined. Results: All Chl. FPs changed along drought stress gradient and
phenological phases, with significant changes at SP. Discussion: A significant change in the mentioned
parameters explains the happening of severe photoinhibition because of photo-inactivation of the PSII
reaction centers, or expresses thermal dispersion from the antenna pigment-protein compound. A remarkable
alteration in pigment content was noticed at the SP. Decrease in the chlorophyll content under drought stress
can be due to a reduction in synthesis of pigment complexes encoded by the cab gene family or destruction of
light harvesting chlorophyll ‘a’ or ‘b’ pigment protein systems. Conclusions: we can say that Z.
eurypterumcan protects the PSII reaction center from damage at the middle stage of drought stress (end of
July) and can be qualified as a drought tolerant species.