Does polyamine seed pretreatment modulate growth and levels of some plant growth regulators in hexaploid wheat (Triticum aestivum L.) plants under salt stress?

The effect of seed presowing treatment with polyamines (2.5 mM putrescine, 5.0 mM spermidine and 2.5 mM spermine) on growth and internal levels of different plant growth regulators in two spring wheat (Triticum aestivum L.) cultivars MH-97 and Inqlab-91 was studied. The primed seeds of each treatment and non-primed seeds were sown in a field in which NaCl salinity of 15 dS m was developed. Although all three polyamines were effective in improving grain yield in both cultivars under saline conditions, the effect of spermine (Spm) was more pronounced. All priming agents reduced leaf free abscisic acid (ABA) levels in MH-97 as compared with untreated plants under saline conditions, but putrescine (Put) priming caused a maximum increase in leaf ABA concentration in MH-97 under saline conditions. In contrast, in Inqlab-91, Put proved to be very effective in increasing free indoleacetic acid (IAA) concentration under saline conditions. Spermidine (Spd) and Spm were very effective in enhancing salicylic acid (SA) concentration in both MH-97 and Inqlab-91 under saline conditions. Leaf free Put concentration was higher in plants of MH-97 raised from seeds treated with Spd under saline conditions. In contrast, all priming agents decreased leaf Put concentration compared with non-priming in Inqlab-91 under saline conditions. Plants of both cultivars raised from seeds treated with Put had the maximum Spm levels under saline conditions. Overall, the beneficial effects of priming agents (polyamines) were cultivar specific. Physiologically, the beneficial effect of pre-sowing treatment with Spm on grain yield in both cultivars may be attributed to altered hormonal balance.