Malfunctioning stomata in vitreous leaves of carnation ( Dianthus caryophyllus) plants propagated in vitro; Implications for hardening

Abstract

Carnation ( Dianthus caryophyllus L. var. ceris royallete) shoot apices cultured in liquid or semi-solid proliferation media often develop into vitreous plants with translucent or succulent leaves. These leaf types lack cuticular waxes and develop stomata with non-functioning guard cells. In the present work, the guard cells were highly variable in morphology and size. Stomata in epidermal peels from vitreous leaves did not close in response to darkness, abscisic acid (ABA) or Ca 2+, signals which usually cause the closure of functional stomata. In functional stomata, reduction in the guard cell's turgor and concomitant reduction in their volume and a change in shape causes closure of the stomatal pore. Stomatal guard cells of translucent and succulent leaves did not close even when the turgor was reduced to zero by plasmolysis. Guard cell osmotic potential increased in the normal fashion in response to 10 −4 M ABA indicating that the protoplasts of the non-functional stomata respond to the closing signal but the stomata fail to close. These results indicate that the cause for the failure of stomata from vitreous leaves to close lie mainly in the guard cell wall and not in the protoplast. Apices cultured in media with reduced minerals but with elevated Ca 2+ developed normal leaves with functioning guard cells. Reduced humidity in the culture tube and higher agar concentration in the medium, induced normal leaf and stomata development with improved carnation plantlet survival after transplanting.