Abstract:
Seed germination is one of the critical and sensitive stages of plant development and is affected
by stresses. Polyamines (PAs) are aliphatic amine growth regulators playing key roles in plant
development and defense. Diamine putrescine (Put), triamine spermidine (Spd), and tetramine
spermine (Spm) are the most common free PAs in plants. The study was conducted to explore the
benefits of seed priming with PAs on seed germination under stress conditions; for tomato
(Solanum lycopersicum L.) under water stress and for rice (Oryza sativa L.) under Aluminium (Al3+)
stress. Tomato and rice seeds were surface sterilized and primed with 50μM and 1mM PAs
solutions respectively or with sterile distilled water (controls). Pre-soaked 10-15 seeds were
placed on filter papers and water stress for tomato seeds was enforced with 0.5% and 1%
polyethylene glycol-6000 (PEG) and control (PEG free) solution while Al3+ stress for rice was
induced by 250 µM and 750 µM of AlCl3 solutions (pH 4.2) and control (Al free). Germination
percentage, mean germination time and α-amylase activity of germinating seeds was assessed.
After 04 days of sowing, percentage of tomato seed germination was reduced in 0.5% and 1% PEG
in comparison to control. Percentages of germination of control, Put, Spd and Spm-primed tomato
seeds were 43%, 53%, 62% and 63%, respectively in 0.5% PEG and in 1% PEG the percentages of
germination were 37%, 52%, 60% and 62%, respectively. PA-untreated control rice seeds showed
significantly reduced germination (p< 0.05) at 250 µM Al3+ (14%) and 750µM Al3+ (4%) compared
to germination at Al-free growth conditions (26%) after 03 days of sowing. Put, Spd and Spm primed seeds showed enhanced germination both under Al-stressed and control conditions.
Under 750 µM of Al3+, Put (28%), Spd (38%) and Spm (32%) primed seeds showed significantly
higher percent germination in comparison to control (4%). Relatively higher α-amylase activities
in Spd and Spm-primed tomato seeds were observed than that of control at 04 days of tomato
seed germination in 1% PEG. Germinating PA-primed rice seeds indicated increased α-amylase
activity compared to the PA-untreated controls under Al stress. These results exhibited that PA
priming enhances germination of tomato seeds under water stress and rice seeds under Al stress
suggesting positive effects of exogenous PA treatment in seed germination under these stress
situations.
