Hormone and phenol levels during germination and osmopriming of tomato seeds, and associated variations in protein patterns and anatomical seed features

Abstract

Seeds of tomato (Lycopersicon esculentum Mill., variety Castle Rock) were osmoprimed in polyethylene glycol 6000 (PEG; 20%) or K 2 HPO 4 (200 mM) solution for 8 hours, 3 days or 7 days, while another group of seeds were left in water for the same periods. The GA 3 /ABA ratio was the most important hormone factor, which promoted germination in seeds soaked in H 2 O and led to improved germination performance. This ratio showed slight variations between hydroprimed and osmoprimed seeds after 8 hours, but afterwards, from 3 to 7 days, it was gradually increased in the osmoprimed seeds and was substantially elevated in seeds germinating in H 2 O. Changes in the concentrations of phenolic compounds suggested their possible role in germination silencing in the osmoprimed seeds, but at relatively low concentrations. Protein patterns showed no marked variations in hydroprimed and osmoprimed seeds after 8 hours, but different types were observed, particularly after 7 days. A comparison of the protein banding patterns of seeds after 1 day and 7 days in the osmoconditioning solutions (PEG or K 2 HPO 4 ), H 2 O, GA 3 or ABA showed certain treatment-specific protein bands, particularly in PEG and ABA solutions. Longitudinal sections of seeds (after 3 days) showed lysis of the micropylar endosperm and radicle protrusion in H 2 O or GA 3 , whereas in PEG or K 2 HPO 4 solution the radicle expanded inside the seed and the micropylar endosperm was completely intact. In ABA solution, the whole endosperm was compact and the seed became extensively desiccated.

Seed Priming: New Comprehensive Approaches for an Old Empirical Technique

“…Priming-induced increase in germination may be associated to a change in plant hormone biosynthesis and signaling. Priming has been reported to increase gibberellins (GA)/abscisic acid (ABA) ratio [75], and this may be a direct consequence of a priming impact in gene expression pattern [76]. A more uniform GA endogenous concentration in primed seeds may help to synchronize endosperm weakening, embryo cell elongation, and reserve mobilization [77].…”

“…Frequently, such improvement is obvious just after emergence at the seedling level, but progressively disappears at the adult stage. For example, some young plants issued from priming treatments displayed improvement of resistance to chilling [84], low temperature [75], salinity [43,102], high temperature [80], drought [24,65,103], and UV exposure [82]. Some interesting studies also demonstrated that priming may afford resistance to biotic stresses such as Fusarium oxysporum in tomato [104], viral disease in Brassica rapa [105], and downy mildew in pearl millet [106].…”

Different Modes of Hydrogen Peroxide Action During Seed Germination

“…Priming enhanced germination performance may be considered a result of advanced germination metabolism processes ( Soeda et al, 2005 ) involving more efficient respiratory pathways ( Li et al, 2010 ; Sun et al, 2011 ), enhanced antioxidant activity ( Bailly et al, 1998 , 2000 ; Posmyk et al, 2001 ; Chen and Arora, 2011 ; Yacoubi et al, 2011 ), initiated repairing processes ( Balestrazzi et al, 2011 ; Kibinza et al, 2011 ), and altered phytohormonal balance ( El-Araby et al, 2006 ). Higher expressions of genes and proteins involved in water transport, cell wall modification, cytoskeletal organization, and cell division and increases in protein synthesis potential, post-translational processing capacity, and targeted proteolysis have been linked to the advanced germination of primed seeds ( Gao et al, 1999 ; Gallardo et al, 2001 ; Chen and Arora, 2013 ; Kubala et al, 2015a ).…”

Metabolic Processes During Seed Germination

“…On the other hand, salts and hormone priming affect not only the seed hydration but also other germination-related processes due to absorption of exogenous ions/hormones, consequently confusing the effects of imbibition versus that of ions/hormones. Improvement germination performance of primed seeds may be considered a result of advanced metabolism processes [134] including enhancement each of the efficiency of respiration [135] and antioxidant activity [136], initiation of repairing processes [137] and alteration phytohormonal balance [138]. Also, improvement of germination performance may be linked to higher expressions of gene sand proteins involved in water transport, cell wall modification, cytoskeletal organization, and cell division and increases in protein synthesis potential, post-translational processing capacity, and targeted proteolysis have been linked to the advanced germination of primed seeds [139].…”