ABSITRACT Suboptimnal levels of phospborus (P) strongly inhibited leaf expansion in young cotton (Gousypium hirstum L.) plants during the daytime, but had little effect at night. The effect of P was primarily on cell expansion. Compaed to plants grown on high P, plants grown on low P had lower leaf water potentials and transpiration rates, and greater diurnal fluctuations in leaf water potential. Hydraulic conductances of excised root systems and of intact transpiring plants were determined from curves relating water flow rate per unit root length to the pressue differential across the roots. Both techniques showed that low P significantly decreased root hydraulic conductance. The effects of P nutrtion on hydraulic conductance preceded effects on leaf area. Differences in total root length, shoot dry weight, and root dry weight all occurred well after the onset of differences in kaf expansion. The data strongly inicate that low P limits leaf expansion by decreasing the hydraulic conductance of the root system.In dicotyledonous plants, growth on suboptimal levels of N is characterized by a specific inhibition of leaf expansion (18)(19)(20). Low N decreases plant hydraulic conductance, thereby lowering the leaf O.' during the daytime when transpiration generates large fluxes of water (18,19). This increased water deficit, in turn, inhibits leaf expansion (18,19). One consequence of this alteration is an increased root: shoot ratio (21). Low P also decreases hydraulic conductance (17, 23) and increases the root:shoot ratio (4, 13). These parallels between effects of N and of P suggest that hydraulic conductance may limit growth in Pdeficient plants as it does in N-deficient plants. Here we present evidence that effects of P nutrition on hydraulic conductance determine its effects on growth of cotton plants.MATERIALS AND METHODS Plant Growth Conditions. Cotton (Gossypium hirsutum L. cv Deltapine 70) plants were grown in a growth chamber. In early experiments, plants were grown in 14-L pots containing sand.The pots were watered three times weekly with a modified halfstrength Hoagland solution containing either 0.5 mM Pi as KH2PO4 (normal P) or 0.5, 0.25, 0.125, 0.0625, or 0 x normal P levels. In later experiments, plants were grown in liquid nutrient solution. Seeds Cell size in the upper epidermis of a leaf was determined by spraying an acrylic resin on the surface, peeling it offafter drying, and using its negative image of the surface for cell counts under a microscope (20
follows:Nitrogen nutrition strongly affected the growth rate of young sunflower (Helianthus annuus L.) leaves. When plants were grown from seed on either of two levels of N availability, a 33% decrease in tissue N of expanding leaves was associated with a 75% overall inhibition of leaf growth. Almost all of the growth inhibition resulted from a depression of the daytime growth rate. Measurements of pressure-induced water flux through roots showed that N deficiency decreased root hydraulic conductivity by about half. Thus, N deficiency lowered the steady-state water potential of expanding leaves during the daytime when transpiration was occurring. As a result, N-deficient leaves were unable to maintain adequate turgor for growth in the daytime. N deficiency also decreased the hydraulic conductivity for water movement into expanding leaf cells in the absence of transpiration, but growth inhibition at night was much less than in the daytime. N nutrition had no detectable effects on plastic extensibility or the threshold turgor for growth.where Jg is water flux associated with growth (cm3 s-'), Wis water content of the leaf under study (cm3), and k (=dW/dl, cm2) is an empirically determined coefficient. The water uptake associated with growth can also be described by the transport equation: A major consequence of N deficiency in plants is a decreased growth rate. Watson (26,27) concluded that N deficiency limits growth primarily by limiting the rate of leaf area increase, rather than the rate of dry matter accumulation per unit leaf area. This conclusion is supported by numerous studies using both growth analysis and direct measurements of photosynthesis (1,8,9,19).Much of this effect on leaf area can be ascribed to effects on cell expansion rather than cell division (18, 21), but there are no reports which might suggest an explanation. Cell growth is commonly described by the relationship (11):
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.