Evidence of Phytochrome Mediation in the Low-pH-Induced Root Hair Formation Process in Lettuce (Lactuca sativa L. cv. Grand Rapids) Seedlings

Abstract

The role of light for the low-pH-induced root hair formation process in lettuce seedlings was reported. A high rate of root hair formation was induced by low-pH (pH4.0) treatment under continuous white light, while no root hairs were observed in the dark irrespective of pH conditions. The fluence requirement for root hair initiation was lower than that for root hair elongation, indicating that two different mechanisms operate in the photoinduction of mature root hairs. With regard to root hair initiation, red and blue light were equally effective, even more than white light, while l i e initiation was obtained with far-red light. The fluence response curve for red and blue light was biphasic and showed two maxima at about 100 and 1,OOO Jm2. The inductive effect of 100 J m 2 red light could be partially reversed by subsequent far-red light only one time. On the other hand, the inductive effect of 1,OOO Jm-* red liht was partially reversed by subsequent far-red light irradiation at least twice. These results indicate the involvement of phytochrome in this response. The inductive effect of blue light was repeatedly reversed by subsequent far-red light irradiation, suggesting that the blue-light induction was mainly mediated by phytochrome.

Isolation and Characterization of the ACC Synthase Genes from Lettuce (Lactuca sativa L.), and the Involvement in Low pH-Induced Root Hair Initiation

“…In our previous study, we found that root hair formation occurred on seedlings that were grown at pH 4.0 under white light, but not on seedlings in the dark even when they were grown at pH 4.0 (De Simone et al 2000). This suggests that light is essential for the process of root hair initiation.…”

“…6 The effects of light on ethylene production from seedlings. Following pre-culture at pH 6.0 in the dark, the seedlings were cultured at pH 4.0 in the dark for 3 h to maximize sensitivity to light (De Simone et al 2000). The seedlings were subjected to red (open square), blue (open triangle), or white (open circle) light for 30 min, and then returned to the dark condition.…”

“…5 The effects of light on the mRNA expression of Ls-ACS1 and Ls-ACS2. Following pre-culture at pH 6.0 in the dark, the seedlings were cultured at pH 4.0 in the dark for 3 h to maximize sensitivity to light (De Simone et al 2000), and then subjected to red, blue or white light for 30 min. Control seedlings were maintained in the dark at pH 4.0 after the pre-culture.…”

“…Seeds were sown on nylon mesh under the green safety light (De Simone et al 2000), and pre-cultured at pH 6.0 in the dark for 24 h. They were then transferred to pH 4.0 medium under the green safety light, and incubated for 3 h in the dark before light irradiation, since seedlings showed maximum light-sensitivity 3 h after the pH was lowered (De Simone et al 2000). The seedlings were then irradiated with red light of 600-700 nm (3.29 W m -2 ), blue light at 380-550 nm (3.09 W m -2 ) or white light at 380-760 nm (2.95 W m -2 ) for 30 min at pH 4.0.…”

“…These results suggest that ethylene and auxin positively regulate root hair formation in lettuce seedlings. Light irradiation was also shown to be essential for low-pH-induction of root hair formation, since dark-grown seedlings did not form root hairs, even at pH 4.0 (De Simone et al 2000).…”