The Hong Mang Mai wheat cultivar is tolerant to deep-sowing conditions because it has an elongated first internode that is sensitive to gibberellin (GA(3) ). The cells in the GA-treated first internodes were approximately 4.2 mm long, twice as long as the untreated Hong Mang Mai first internode cells. The elongation of the first internode of Hong Mang Mai, particularly when treated with GA(3) , was accompanied by remarkable spiral growth. In contrast, the first internodes of the GA-insensitive cultivar Norin 10 did not exhibit GA(3) -induced elongation or spiral growth. The walls of the first internode cells of GA(3) -treated Hong Mang Mai seedlings showed increased extensibility and higher (1-->3), (1-->4)-beta -d-glucanase activity, autolysis and glucan contents than the cell walls of untreated Hong Mang Mai first internodes. The changes in the cell wall extensibility due to GA(3) treatment correlated strongly with the GA(3) -induced changes in cell wall glucan content, autolysis, and glucanase activity. GA(3) -treated Hong Mang Mai seedlings showed elevated expression of Glucanase EI gene in the first internode compared to GA(3) -treated Norin 10. Thus, GA aids first internode elongation in Hong Mang Mai by enhancing glucan turnover and thus increasing cell wall loosening. The spiral growth of the first internode also helps the plant elongate against soil resistance, thereby promoting the deep-sowing tolerance of this cultivar.
