Melatonin Applied by Hydropriming as a Biostimulator Improving Sweet Corn (Zea mays L.) Seedling Growth in Abiotic Stress Conditions

Sweet corn (Zea mays L cv. Gama) seed hydropriming effects on germination and subsequent seedling growth under suboptimal conditions (chilling temperatures or toxic copper concentration) were investigated. Biochemical stress markers, contents of chlorophylls and phenolic compounds (PhC) were also estimated. Seeds were hydroprimed (H) or hydroprimed with melatonin (Mel) water solutions (HMel) at concentrations: 25, 50, 100 and 500 mu M. Mel contents in the seeds before and after priming were determined using HPLC-EC. 90%-100% sweet corn seeds germinated at 25, 15 and also at 10 degrees C. At 25 degrees C this result was obtained during first two days, while at 15 degrees C and at 10 degrees C two and four days of imbibition without radical axe growth (lag-phase) were observed, respectively. H, HMel 25 and. HMel 50 shrunk the lag-phase to one day at 15 degrees C and two days at 10 degrees C. HMel 25 and HMel 50 markedly accelerated the rate of seed germination. Positive effect of H on seed germination was also observed during subsequent seedling growth. Under optimal conditions the seedlings from HMel 25 and HMel 50 seeds developed faster. Toxic copper ion (Cu(+2)) concentration (2.5 mM) did not affect corn seed germination but drastically reduced seedling growth and blocked their regeneration. On the basis of the biochemical analyses such as chlorophyll and PhC contents it was noted that only in the case of seedlings grown from the seeds previously H, HMel 25 and HMel 50 regeneration processes after chilling and Cu(+2) stresses went well. There is still lack of information clearly explaining the role of MEL in plant physiology. This molecule acts multidirectionally and usually is allied to other compounds (e.g. PhC) its potential as a degrees phytobiostimulator will be discussed.