Abscisic acid Abscisic acid suppresses cell growth. Abscissic acid also appears to be involved in stomatal opening and closing. It may have a role in root gravitropism. In turn, these changes in phytochromes stimulate or repress the flowering of plants. There are two categories of plants with respect to flowering.
Short day plants flower in response to long nights .
Long day plants flower in response to short nights . During daylight, plants are performing photosynthesis at a greater rate than cellular respiration if their stomata are open. For this to occur, there must be a net input of carbon dioxide and water in the leaves. Water enters the plant via osmosis in the roots. It travels up the xylem to the leaves.