Escape of etiolated hypocotyls of cotton () from the unilateral high intensity blue light after being pulled out from the soil.

Plant stems grow towards the incident light in response to unilateral blue light to optimize photosynthesis. However, our findings reveal that unilateral high-intensity blue light (HBL) triggers backlit lodging in etiolated cotton (Gossypium hirsutum ) hypocotyls when they are pulled approximately 1.5cm from the soil. Phenotypic analysis indicated that stomata on the lit side were open, while those on the shaded side were closed under unilateral HBL. To investigate the relationship between stomatal movement and backlit lodging, we applied abscisic acid (ABA), hydrogen peroxide (H2 O2 ), and lanthanum chloride (LaCl3 ) to the lit side, and cytokinins (6-BA) and ascorbic acid (ASA) to the shaded side. Results showed that all these treatments inhibited the backlit lodging phenomenon, specifically, ABA, H2 O2 , and LaCl3 reduced stomatal opening on the lit side, while 6-BA and ASA enhanced stomatal opening on the shade side. These results demonstrate that HBL-induced asymmetrical stomatal opening on the lit and shade side of hypocotyl supports the backlit lodging phenomenon. Notably, maize (Zea mays ), which lack stomata in the hypocotyl did not exhibit HBL-induced backlit lodging, whereas soybean (Glycine max ), which has stomata in its etiolated hypocotyl, displayed a similar phenotype to that of cotton. Additionally, while both red light and low-intensity blue light (LBL) can induce stomatal opening, they do not trigger the backlit lodging phenomenon. These findings suggest that backlit lodging is a unique HBL-dependent response, but the mechanism need further investigation.