Photosynthesis, chlorophyll fluorescence, inorganic ion and organic acid accumulations of sunflower in responses to salt and salt-alkaline mixed stress

Abstract

Sunflowers were treated with mixing proportions of NaCl, Na 2 SO 4 , NaHCO 3 , and Na 2 CO 3 . Effects of salt and saltalkaline mixed stress on growth, photosynthesis, chlorophyll fluorescence, and contents of inorganic ions and organic acids of sunflower were compared. The growth of sunflower decreased with increasing salinity. The contents of photosynthetic pigments did not decrease under salt stress, but their contents decreased sharply under salt-alkaline mixed stress. Net photosynthetic rates, stomatal conductance and intercellular CO 2 concentration decreased obviously, with greater reductions under salt-alkaline mixed stress than under salt one. Fluorescence parameters showed no significant differences under salt stress. However, maximal efficiency of PSII photochemistry, photochemical quenching coefficient, electron transport rate, and actual PSII efficiency significantly decreased but non-photochemical quenching increased substantially under salt-alkaline mixed stress. Under salt-alkaline mixed stress, sunflower leaves maintained a low Na + -and high K + status; this may be an important feature of sunflower tolerance to salinity. Analysis of the mechanism of ion balance showed that K + but not Na + was the main inorganic cation in sunflower leaves. Our results indicated that the change in organic acid content was opposite to the change of Cl -, and the contribution of organic acid to total charge in sunflower leaves under both stresses decreased with increasing salinity. This may be a special adaptive response to stresses for sunflower. Sunflower under stress conditions mainly accumulated inorganic ions instead of synthesizing organic compounds to decrease cell water potential in order to save energy consumption.

Salt sensitivity in chickpea: Growth, photosynthesis, seed yield components and tissue ion regulation in contrasting genotypes

“…Such observations of higher A and g s in saline conditions by tolerant over sensitive genotypes, have been reported in soybean (Lu et al, 2009) and rice (Moradi and Ismail, 2007). Moreover, increased WUE in saline conditions was evident in tolerant genotypes of sunflower (Liu and Shi, 2010) and wheat (Yang et al, 2008), as found here for Genesis836 in chickpea, possibly assisting these genotypes to cope with reduced leaf water potential in saline conditions. Salt stress can affect A in plants via stomatal closure leading to decreased CO 2 availability or by changing the photosystems and photosynthetic metabolism (Chaves et al, 2009).…”

Deciphering the possible mechanism of exogenous NO alleviating alkali stress on cucumber leaves by transcriptomic analysis

“…Accumulation of organic acids was one regular defense response in plants exposed to stress conditions, especially in salt and alkaliinduced osmotic stress or nutrient deficiency (Li and Shi, 2010;Carvalhais et al, 2011). In the present study, SNP treatment significantly increased contents of acetate, malate and citrate in cucumber leaves under alkali stress, which was exactly in accordance with the enrichment of organic acid metabolic process (GO: 0006082) and carboxylic acid biosynthetic process (GO: 0046394).…”

Global proteomic mapping of alkali stress regulated molecular networks in Helianthus tuberosus L.

“…Accumulating evidence suggests that photosynthesis is greatly inhibited under excessive sodium carbonate conditions via the decrease of chlorophyll biosynthesis and photosystem II efficiency (Yang et al 2008a;Liu and Shi 2010;Bu et al 2012). Our proteomic analysis showed 20 photosynthetic proteins were differentially expressed in H. tuberosus subjected to Na 2 CO 3 stress.…”

“…Studies have shown that alkali stress also significantly affects photosynthesis and photosynthetic electron transport. In rice, sunflower and thirty switchgrass, alkali stress caused a sharp reduction in photosynthetic parameters and chlorophyll fluorescence (Liu and Shi 2010;Bu et al 2012;Hu et al 2015). The same situation occurred in halophyte Chloris virgate except the net photosynthetic rate (P N ) was increased slightly under moderate alkali stress (Yang et al 2008a).…”