Assessment of photosynthetic capacity of two blackberry cultivars subjected to salt stress by the JIP fluorescence test

BACKGROUND: Salt stress has recently emerged as one of the most significant abiotic stresses with negative impact on crop production. Photosynthesis is a vital biochemical process in plants, very sensitive to environmental constraints, including salt stress. OBJECTIVE: The aim of this study was toevaluate the impact of salt stress on photosystem II in the leaves of blackberry cultivars (Rubus fructicosus L.). METHODS: Two blackberry cultivars (Thornfree and Boysen) were exposed to salt stress (20, 40, and 60 mM NaCl) for 28 days in in vitro culture. The photosynthetic activity was evaluated by probing chlorophyll a fluorescence (JIP test) and photosynthetic pigments. RESULTS: The maximum quantum yield of PSII (Fv/Fm), performance indexes (PIABS and PItotal), and photosynthetic driving force (DFABS) were greatly affected by salt stress in the leaves of Boysen cultivar. Lower photosynthetic efficiency was confirmed by the increased values of absorption flux per RC (ABS/RC), trapping flux per PSII RC (TR0/RC), dissipation flux per RC (DI0/RC), decreased values of chlorophyll and carotenoid contents, disruption in the interaction between the light-harvesting complex and the core proteins of PSII, as well as disruption of the oxygen-evolving complex. CONCLUSIONS: The provided informations suggest that the photosynthetic apparatus of Thornfree cultivar was found to be more tolerant to salt stress compared to Boysen.