Net rates of photosynthesis (PN) saturated by irradiance of >500 μmol m-2 s-1 (PAR) significantly decreased in water-stressed potato (Solanum tuberosum L. cv. Kufri Sindhuri) plants. The quantum yield of photochemical energy conversion (Fv/Fm), relative electron transport rate (ETR), and photochemical quenching (Qp) exhibited a parallel decline at high irradiance. A slight decrease in relative water content (RWC) was accompanied by a drastic decline in leaf water potential (Ψw) from -0.2 to -1.0 MPa. Dehydrated leaves showed an increase in the amount of total soluble sugars per unit leaf area which inhibited the photosynthesis in a feedback manner. After rewatering, PN and Fv/Fm were restored to the values of control plants within 24 h, and the restoration was accompanied by a proportionate lowering of content of total soluble sugars in the leaves. and P. S. Basu, Ashoo Sharma, N. P. Sukumaran.
Various physiological characteristics of Cj and C4 plants (14 species) grown along a salinity gradient were studied. The majority of plants occupying salt-marshes were succulent chenopods, mainly C4 annuals. The ash content of assimilating organs of plants was higher and osmotic potential lower in species grown under increasing soil salinity. The plants of the NADP-ME group accumulated more K than Na. Large amounts of Na"^ and CT characterized the NAD-ME plants and perennial C3 plants from sites with high soil salinity, Net photosynthetic rate (P^) and chlorophyll content were decreased in species grown under high salinity. Dark respiration was depressed by salinity to a lesser extent than P^.
Tomato seeds exposed to space conditions for nearly six years on board the Long Duration Exposure Facility (LDEF) satellite were subsequently germinated and the resultant seedlings grown on earth under controlled conditions for analysis. Photosynthesis, biomass, and water relations were compared between mature plants grown from earth-based control seeds and space-exposed seeds under both well-watered and drought-stressed conditions. No consistent significant differences in photosynthesis and water relations were observed in the two sets of plants at any level of drought stress. Fruit production, however, though limited and variable, was significantly greater in plants grown from space-exposed seeds than in plants grown from earth-based seeds. Overall, exposure of seeds to space had only minor effects on the physiology and growth of plants grown from such seed. and M. S. Marmor, C. E. Martin.
The effects of potassium nutrition [0, 6.25, 12.50, 25.00 g(K) m-2 of K2SO4 or KCl] on gas exchange characteristics and water relations in four cultivars (CIM-448, CIM-1100, Karishma, S-12) of cotton were assessed under an arid environment. Net photosynthetic rate (PN) and transpiration rate (E) increased with increased K supply. The leaf pressure potential (Ψp) increased significantly by the addition of 25.00 g(K) m-2 compared to zero K level. The water use efficiency (PN/E) was improved by 24.6 % under the highest K dose compared to zero K. There were positive correlations (0.99**, 0.98**, 0.95**, 0.97**) between K-doses and PN, E, Ψp, and PN/E, respectively. and H. Pervez, M. Ashraf, M. I. Makhdum.
Typical chestnut thylakoid extracts isolated by mechanical disruption of leaf tissues had an equivalent of 0.28 kg m-3 chlorophyll (Chl) which is six times less than in thylakoids obtained from spinach, although Chl content in leaves was only half as small. According to optical microscopy, the vesicles showed a good integrity, exhibiting at 21 °C a high capacity of photon-induced potential membrane generation, which was demonstrated by the almost full 9-amino-6-chloro-2-methoxyacridine fluorescence quenching in a hyper-saline medium containing 150 mM KCl and having osmotic potential of -1.5 MPa. The half-time of the thylakoid potential generation was 11.7 s with the time of dissipation around 8.9 s. In such conditions, spinach thylakoids showed an increased swelling and also differences in the half-time generation which was almost four times faster than was observed in chestnut. However, when spinach thylakoids were incubated in a typical hypo-saline medium without KCl with osmotic potential -0.8 MPa, no additional swelling was observed. Consequently the half-time of potential dissipation was 35 s. Studies with nigericin suggested a chestnut thylakoid ΔpH significantly smaller than that observed in spinach, which was confirmed by the measurements of the ATP driven pumping activity. and J. Gomes-Laranjo ... [et al.].
The objective of this study was to evaluate the response of the giant reed (Arundo donax L.) to drought stress at early stages, as well as to determine the effects of limited soil water availability on plant growth, gas exchange, and water-use efficiency. Plantlets of a commercial clone were grown in a greenhouse under two water treatments: at 100% of field capacity and progressive drought for 66 days (until 20% of field capacity). Soil water content, leaf elongation rate, plant water consumption, and gas-exchange parameters were measured throughout the experiment. Total plant biomass, leaf water, and osmotic potential were determined at the end of the experiment. Plant growth and leaf gas-exchange parameters were significantly affected by soil water availability, but only when it was below 40% of field capacity. At early stages, Arundo donax showed drought stress acclimation due to leaf plasticity, stomatal regulation, and osmotic adjustment., A. Romero-Munar, E. Baraza, J. Cifre, C. Achir, J. Gulías., and Obsahuje bibliografii
Maize plants of CPB2 and CPB8 hybrids were kept under water deficit for 22 d. In the CPB8 hybrid, leaf rolling initiated at the 9th d of water deficit period, while in CPB2 hybrid it was at the 15th d. Both hybrids showed leaf rolling initiation at the same leaf water potential, ΨW of -0.480±0.095 MPa. At leaf rolling initiation, the leaf osmotic potential, ΨS was -0.730±0.085 MPa in CPB8 and 0.630±0.110 MPa in CPB2. The leaf temperature and stomatal conductance were higher in CPB8 than in CPB2. Values of leaf ΨW, ribulose-1,5-bisphosphate carboxylase activity, chlorophyll content, and specific leaf area were similar in both hybrids. Phosphoenolpyruvate carboxylase activity and protein content were lower in the CPB2 hybrid than in CPB8. In both hybrids leaf rolling initiation was associated with: (1) higher leaf temperature, with leaf rolling effect related to leaf temperature reduction, and (2) lower leaf ΨS, related to osmotic adjustment as an additional component of drought-tolerance strategy. and D. Fernandez, M. Castrillo.
In order to address the question of how elevated CO2 concentration (EC) will affect the water relations and leaf anatomy of tropical species, plants of Jatropha gossypifolia L. and Alternanthera crucis (Moq.) Bondingh were grown in five EC open top chambers (677 μmol mol-1) and five ambient CO2 concentration (AC) open top chambers (454 μmol mol-1) with seasonal drought. No effect of EC was found on morning xylem water potential, leaf osmotic potential, and pressure potential of plants of J. gossypifolia. In A. crucis EC caused a significant increase in morning xylem water potential of watered plants, a decrease in osmotic potential, and an increase of 24-79 % in pressure potential of moderately droughted plants. This ameliorated the effects of drought. Stomatal characteristics of both leaf surfaces of J. gossypifolia and A. crucis showed time-dependent, but not [CO2]-dependent changes. In J. gossypifolia the thickness of whole leaf, palisade parenchyma, and spongy parenchyma, and the proportion of whole leaf thickness contributed by these parenchymata decreased significantly in response to EC. In A. crucis EC caused an increase in thickness of whole leaf, bundle sheath, and mesophyll, while the proportion of leaf cross-section comprised by the parenchymata remained unchanged. These effects disappeared with time under treatment, suggesting that acclimation of the leaf anatomy to the chambers and to EC took place in the successive flushes of leaves produced during the experiment. and E. Rengifo, R. Urich, A. Herrera.