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  • Author or Editor: P. Zanamwe x
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The separate roles of ethylene and gibberellins on seed germination have not been clearly established. This has limited full utilisation of these hormones in barley malting. This study was carried out to investigate the roles of gibberellins and ethylene on the germination physiology of ‘Puma’ barley seeds. Germination curves, percent germination, rootlets length and respiration rates of seeds treated with ethylene, 1-methylcyclopropane (1-MCP), gibberellic acid (GA3), daminozide (B-nine), GA3 + ethylene, GA3 + 1-MCP, ethylene + B-nine, 1-MCP + B-nine and the control were compared after 24, 48 and 72 h from soaking, respectively. GA3 and ethylene treatments were used to investigate the effects of increasing endogenous ethylene and GA3 levels, respectively. B-nine and 1-MCP treatments were used to assess the effects of inhibiting gibberellins synthesis and ethylene perception, respectively. Combination treatments were used to assess hormonal interactions. GA3 and ethylene treatments suppressed germination after 24 h, but, had no effect after 48 and 72 h, respectively. B-nine, ethylene + B-nine and 1-MCP + B-nine suppressed germination, rootlet elongation and respiration after 24, 48 and 72 h, respectively. 1-MCP and GA3 + 1-MCP stimulated germination after 24 h, but, had no effect after 48 and 72 h, respectively. GA3 + ethylene treatment suppressed germination and rootlet elongation but stimulated respiration after 24 h. Ethylene suppressed rootlets elongation after 24, 48 and 72 h from soaking, respectively. GA appeared to be the dominant germination hormone, and ethylene, to regulate the rate of germination through suppression of rootlets elongation.

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Treatment of barley grain with gibberellic acid (GA3) during malting promotes abnormal proteolysis and rapid rootlets growth affecting malt quality. This study investigated the potential of ethylene treatment as an alternative by comparing the amylase activity, total starch and total reducing sugars of germinating ‘Puma’ barley seeds treated with ethylene, 1-methylcyclopropane (1-MCP), GA3, daminozide (B-nine), GA3 + 1-MCP, ethylene + B-nine and the control after 24, 48 and 72 h from soaking. Ethylene had no effect on amylase activity. B-nine reduced amylase activity by 16 and 9.6% compared to the control after 48 and 72 h, respectively. The amylase activity of ethylene + B-nine treated seeds was higher (13.3 and 4%) than B-nine treated seeds after 48 and 72 h. This suggest that endogenous GA is important for normal amylase activity and, ethylene stimulates amylase activity where GA synthesis is inhibited. Ethylene and GA3 treatments reduced starch (83.3 mg g−1 and 76.7 mg g−1, respectively) and increased reducing sugars (16.0 and 17.1 µg ml−1, respectively) compared to the control (115.3 mg g−1 starch and 12.1 µg ml−1 reducing sugars) after 72 h. It was concluded that, ethylene may replace GA3 treatment without interfering with starch changing processes during barley malting.

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