Growth, photosynthesis and antioxidant enzyme modulations in broccoli (Brassica oleracea L. var. italica) under salinity stress

Abstract

Soil salinity is one of the major concerns that pose serious threats to vegetables and other crops worldwide. The present study was carried out to identify morphological, physiological and biochemical markers that broccoli plant may use as adaptive mechanisms to cope with high NaCl stress. Broccoli plants were grown in a pot culture and exposed to NaCl salinity stress for six weeks. Five levels of NaCl; 0, 20, 40, 60, and 80 mmol L − 1 were established using saline irrigation water. Increased soil salinity led to the increased Na+ and Cl– accumulation which inhibited Ca+, K+, Mg2+, NO3–, total P and PO43– concentrations both in leaves and roots. Moreover, increased NaCl salinity decreased the plant leaf area, shoot length, root length, and shoot and root dry weights, whereas enhanced the antioxidant enzymatic activities like superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). Leaf chlorophyll in the form of light energy conservation rate (Fv/Fm) and coefficients of photochemical quenching (qP) and (qL) were significantly affected by increasing the salinity levels. Likewise, NaCl salinity negatively affected the linear electron flow (LEF) and the activity of photosystem-II. Non-photochemical quenching (NPQt) in all stress treatments was significantly improved as compared to the control. In general, 60 mmol L − 1 NaCl level was considered as a threshold for broccoli cultivation under saline irrigation. In conclusion, salt stress primarily controlled the leaf photosynthetic machinery, stimulated redox homeostasis and enhanced the activities of antioxidant enzymes, which enabled broccoli plants to tolerate medium level of NaCl stress.