Characterization of stomata on floral organs and scapes of cut ‘Real’ gerberas and their involvement in postharvest water loss

Abstract

Stomata present on leaves are the main channels for water vapor exchange between the plant and atmosphere, and contribute to water loss of cut flowers. Although cut gerberas (Gerbera jamesonii Bolus) are commonly composed of a terminal composite floral head and a scape, and have no leaves, they are also prone to severe water deficits, presumably resulting from water loss exceeding water uptake. We have investigated the distribution and characteristics of stomata of cut ‘Real’ gerberas, and their response to light and abscisic acid (ABA) treatments, to increase understanding of their functionality in postharvest water loss. Stomata were widely distributed on various parts of floral organs and the scape in cut gerberas, including the lower epidermis of the ray floret petals, trans florets, disc florets, lower epidermis of sepals, and the uppermost and middle parts of scape surfaces. The highest stomatal density was observed on the lower epidermis of sepals. Cut gerberas had the largest stomata on the middle scape surface and the smallest on the surface of the uppermost scape. Nonetheless, the lower epidermis of sepals had the highest relative stomatal area, which was higher than that of the other parts. Additionally, the lower sepal epidermis had the highest maximum stomatal conductance of water vapor (gwmax), and which was higher than that of the lower and upper leaf epidermis. The opening of stomata on various parts of cut gerberas differed in their response to light, and the highest percentage of open stomata and largest aperture were found in the stomata on the lower epidermis of sepals. Changes in water loss in cut gerberas exhibited a distinct circadian rhythm over a four-day vase period with an alternating 12-h light/dark cycle. In the lower epidermis of sepals, ABA painting treatment significantly inhibited stomatal opening and reduced water loss in cut gerberas over a 6 h light period. These findings imply the critical involvement of stomata on the lower epidermis of sepals in water loss of cut gerberas, and improve our understanding of the mechanism underlying their water deficit symptoms.