Developmental Changes in Gas Exchange Activity in Flowers, Berries, and Tendrils of Field-Grown Cabernet Sauvignon

Abstract

Gas-exchange activity and seasonal evolution of some anatomical and biological characteristics linked to CO₂ assimilation processes were analyzed in different green structures on field-grown Cabernet Sauvignon grapevine. Before anthesis, each flower showed 22±3 (mean ± SE) regular stomata in the calyx and 9±3 in the apical part of the caliptrae. Irrespective of position, stomata size was 58±11 µm². Just after anthesis, the stomata density was approximately 7±2 stomata per berry. Young tendrils had 27±4 active and functional stomata per mm², whereas no stomata were found on rachises. Ultrastructural views of the chloroplasts on the flower calyx and young tendrils showed little or no differentiation in distinct grana and stroma lamellae and large and small starch granules, respectively. From two weeks before to eight weeks after anthesis, the flower, grape berry, and tendril did not reach the compensation point and therefore did not fix atmospheric CO₂. In the light, the main photosynthetic role of these organs and structures was the reassimilation of respiratory CO₂. During anthesis, progressive decreases in direct light resulted in a progressive increase in respiration activity. The CO₂ refixation activity decreased during berry and tendril development; this decline paralleled the reduction of chlorophyll a and b, carotenoids, and nitrogen content and the increase of wax weight per unit surface. The transpiration rate in flower, berry, and tendril decreased throughout development and was increased by direct sunlight. These results indicate features that could have important physiological implications when modeling canopy carbon gain of grapevines.