After saturating irradiation for 3 h (SI), the original fluorescence F0 increased while the photosystem 2 (PS2) photochemical efficiency (Fv/Fm) declined significantly. These parameters could largely recover to the levels of dark-adapted leaves after 3 h of subsequent dark recovery. No net loss of the D1 proteins occurred after SI. Soybean and pumpkin leaves had different responses to SI. Low temperature fluorescence parameters, F685 and F685/F735, decreased significantly in soybean leaves but not in pumpkin leaves. Part of the light-harvesting complex LHC2 dissociated from PS2 complexes in soybean leaves but not in pumpkin leaves, as shown by sucrose density gradient centrifugation and SDS-PAGE. The photon-saturated PS2 electron transport activity declined significantly in pumpkin thylakoids but not in soybean thylakoids. In addition, a large amount of phosphorylated D1 proteins was found in dark-adapted soybean leaves but not in dark-adapted pumpkin leaves. Hence at excessive irradiance soybean and pumpkin have the same protective strategy against photo-damage, reversible down-regulation of PS2, but two different mechanisms, namely the reversible down-regulation is related to the dissociation of LHC2 in soybean leaves but not in pumpkin leaves. and Hai-Bo Zhang, Da-Quan Xu.
On the first day after foliar application, chitosan pentamer (CH5) and chitin pentamer (CHIT5) decreased net photosynthetic rate (PN) of soybean and maize, however, on subsequent days there was an increase in PN in some treatments. CH5 caused an increase in maize PN on day 3 at 10-5 and 10-7 M; the increases were 18 and 10 % over the control plants. This increase was correlated with increases in stomatal conductance (gs) and transpiration rate (E), while the intercellular CO2 concentration (Ci) was not different from the control plants. PN of soybean plants did not differ from the control plants except for treatment CH5 (10-7 M) which caused an 8 % increase on day 2, along with increased gs, E, and Ci. On days 5 and 6 the CHIT5 treatment caused a 6-8 % increase in PN of maize, which was accompanied by increases in gs, E, and Ci. However, there was no such increase for soybean plants treated with CHIT5. In general, foliar application of high molecular mass chitin (CHH) resulted in decreased PN, particularly for 0.010 % treated plants, both in maize and soybean. Foliar applications of chitosan and chitin oligomers did not affect (p > 0.05) maize or soybean height, root length, leaf area, shoot or root or total dry mass. and W. M. Khan, B. Prithiviraj, D. L. Smith.
Leaf-root interaction is a critical factor for plant growth during maturation and activity of roots is maintained by a sufficient supply of photosynthates. To explain photosynthate distribution among organs in field crops, the node unit hypothesis is proposed. One node unit consists of a leaf and an upper adventitous root, as well as the axillary organs and the lower adventitious root, which is adjacent to one node. Using 14C as tracer, the carbon distribution system has been clarified using spring wheat, soybean, tomato, and potato. The interrelationship among organs from the strongest to the weakest is in the following order: (1) within the node unit > (2) between the node unit in the same or adjacent phyllotaxy > (3) in the main root or apical organs, which are adjacent to the node unit. Within the node unit, 14C assimilated in the leaf on the main stem tended to distribute to axillary organs in the same node unit. The 14C assimilated in the leaf of axillary organs tended to distribute within the axillary organs, including adventitious roots in the axillary organ and then translocated to the leaf on the main leaf of the same node unit. In different organs of the node unit in the same or adjacent phyllotaxy, 14C assimilated in the leaf on the main stem was also distributed to the organs (node unit) belonging to the same phyllotaxy in dicotyledons, while in monocotyledons, the effect of phyllotaxy on 14C distribution was not clear. Among roots/apical organs and node unit, 14C assimilated in the upper node unit was distributed to apical organs and 14C assimilated in the lower node unit was distributed to roots. Thus the node unit hypothesis of photosynthate distribution among organs is very important for understanding the high productivity of field crops. and M. Osaki ... [et al.].
In soybean seedlings, Cd2+ affected growth and inhibited photosynthesis. Both the length and fresh mass decreased more in roots than in shoots. Cd2+ stress caused an increase in ratio of chlorophyll (Chl) (a+b)/b by 1.3 fold and ratio of total xanthophylls/β-carotene by 3 fold compared to the control. A reduced activity of photosystem 2 by about 85 % measured in Cd2+-treated chloroplasts was associated with a dramatic quenching of fluorescence emission intensity, with a band shift of 4 nm. A major suppression of absorption was accompanied with shift in peaks in the visible region of the spectrum. In Cd2+-treated chloroplasts a selective decline in linolenic acid (18:3), the most unsaturated fatty acid of chloroplasts, paralleled with the ten fold enhancement in ethylene production. A three fold increase in peroxidase activity was found in chloroplasts treated with Cd2+ compared to the control . Addition of 1 mM glutathione (GSH) counteracted all the retardation effects in soybean seedling growth induced by Cd2+. Thus GSH may control the Cd2+ growth inhibition as it detoxifies Cd2+ by reducing its concentration in the cytoplasm and removing hydrogen peroxide generated in chloroplasts.
The effects of enhanced ultraviolet-B (UV-B, 0.4 W m-2) irradiance and nickel (Ni, 0.01, 0.10 and 1.00 mM; Ni0.01, Ni0.10, Ni1.00, respectively) treatment, singly and in combination, on growth, photosynthetic electron transport activity, the contents of reactive oxygen species (ROS), antioxidants, lipid peroxidation, and membrane leakage in soybean seedlings were evaluated. Ni0.10 and Ni1.00 and UV-B declined the growth and chlorophyll content, which were further reduced following combined exposure. Contrary to this, Ni0.01 stimulated growth, however, the effect together with UV-B was inhibitory. Carotenoids showed varied response to both the stresses. Simultaneous exposure of UV-B and Ni as well as UV-B alone reduced the activities of photosystems 1 and 2 (PS1 and PS2) and whole chain activity significantly, while Ni individually, besides strongly inhibiting PS2 and whole chain activity, stimulated the PS1 activity. Both the stresses, alone and together, enhanced the contents of superoxide radical (O2⋅-), hydrogen peroxide (H2O2), malondialdehyde (MDA), electrolyte leakage, and proline content, while ascorbate content declined over control. Individual treatments increased the activities of catalase (CAT), peroxidase, and superoxide dismutase (SOD), but Ni1.00 declined SOD activity significantly. Combined exposure exhibited similar response, however, CAT activity declined even more than in control. Compared to individual effects of UV-B and Ni, the simultaneous exposure resulted in strong inhibition of photosynthetic electron transport and excessive accumulation of ROS, thereby causing severe damage to soybean seedlings. and S. M. Prasad, R. Dwivedi, M. Zeeshan.
In this historical review we summarize discoveries related to the flowering genes in controlling leaf area index (LAI, the leaf area per unit ground area) in sorghum, soybean, or pea crop stands. We also analyze similar work on Arabidopsis and dwarf and intermediate stem height genes in wheat and rice. and G. B. Begonia, M. T. Begonia.
The protective role of light-harvesting complex 2 (LHC2) dissociation from photosystem 2 (PS2) complex was explored by the 5'-p-fluorosulfonylbenzoyl adenosine (FSBA, an inhibitor of protein kinase) treatment at saturating irradiance (SI) in soybean leaves and thylakoids. The dissociation of some LHC2s from PS2 complex occurred after SI treatment, but FSBA treatment inhibited the dissociation as demonstrated by analysis of sucrose density gradient centrifugation of thylakoid preparation and low-temperature (77 K) chlorophyll (Chl) fluorescence. A significant increase in F0 and decrease in Fv/Fm occurred after SI, and the two parameters could largely recover to the levels of dark-adapted leaves after subsequent 3 h in the dark, but they could not recover in the FSBA-treated leaves at SI. Neither the electron transport activity of PS2 nor the D1 protein amount in vivo had significant change after SI without FSBA, whereas FSBA treatment at SI could result in significant decreases in both the PS2 electron transport activity and the D1 protein amount. When thylakoids instead of leaves were used, the PS2 electron transport activity and the D1 protein amount declined more after SI with FSBA than without FSBA. The phosphorylation level of PS2 core proteins increased, while the phosphorylation level of LHC2 proteins was reduced after SI. Also, the phosphorylation of PS2 core proteins could be greatly inhibited by the FSBA treatment at SI. Hence in soybean leaf the LHC2 dissociation is an effective strategy protecting PS2 reaction centres against over-excitation and photodamage by reducing the amount of photons transferred to the centres under SI, and the phosphorylation of PS2 core proteins plays an important role in the dissociation. and Hai-Bo Zhang, Da-Quan Xu.