Department of Botany, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1968 Jul;43(7):1056-62. doi: 10.1104/pp.43.7.1056.
A thermocouple psychrometer that measures water potentials of intact leaves was used to study the water potentials at which leaves grow. Water potentials and water uptake during recovery from water deficits were measured simultaneously with leaves of sunflower (Helianthus annuus L.), tomato (Lycopersicon esculentum Mill.), papaya (Carica papaya L.), and Abutilon striatum Dickson. Recovery occurred in 2 phases. The first was associated with elimination of water deficits; the second with cell enlargement. The second phase was characterized by a steady rate of water uptake and a relatively constant leaf water potential. Enlargement was 70% irreversible and could be inhibited by puromycin and actinomycin D. During this time, leaves growing with their petioles in contact with pure water remained at a water potential of -1.5 to -2.5 bars regardless of the length of the experiment. It was not possible to obtain growing leaf tissue with a water potential of zero. It was concluded that leaves are not in equilibrium with the potential of the water which is absorbed during growth. The nonequilibrium is brought about by a resistance to water flow which requires a potential difference of 1.5 to 2.5 bars in order to supply water at the rate necessary for maximum growth.Leaf growth occurred in sunflower only when leaf water potentials were above -3.5 bars. Sunflower leaves therefore require a minimum turgor for enlargement, in this instance equivalent to a turgor of about 6.5 bars. The high water potentials required for growth favored rapid leaf growth at night and reduced growth during the day.
一种测量完整叶片水势的热电偶湿度计被用于研究叶片生长时的水势。利用向日葵（Helianthus annuus L.）、番茄（Lycopersicon esculentum Mill.）、木瓜（Carica papaya L.）和黄秋葵（Abutilon striatum Dickson）的叶片，同时测量了从水分亏缺中恢复时的水势和水分吸收。恢复过程分为两个阶段。第一阶段与消除水分亏缺有关；第二阶段与细胞扩大有关。第二阶段的特点是水分吸收速率稳定，叶片水势相对恒定。扩大是不可逆的，约 70%，可被嘌呤霉素和放线菌素 D 抑制。在此期间，叶片的叶柄与纯水接触，无论实验持续多长时间，叶片水势都保持在-1.5 至-2.5 巴。不可能获得水势为零的生长叶片组织。因此，叶片与生长过程中吸收的水分的潜力并不处于平衡状态。非平衡是由水流阻力引起的，这种阻力需要 1.5 至 2.5 巴的电位差才能以最大生长所需的速率供水。向日葵叶片只有在水势低于-3.5 巴时才会生长。因此，向日葵叶片在扩大时需要最低的膨压，在这种情况下，相当于膨压约为 6.5 巴。生长所需的高水势有利于夜间叶片的快速生长，并减少白天的生长。
