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- Transport of oxygen in roots of rice (Oryza sativa L.) and of water in developing grape berries (Vitis vinifera L.) (2009)
- 1. Radial oxygen flow in rice roots Measurements of ROL from rice roots grown in either aerated or deoxygenated conditions were combined with root histochemisrty and biochemistry. It was shown that the pattern of ROL from rice roots of stagnantly grown plants correlated with development of the apoplastic barriers in the root peripheral layers. Deoxygenated conditions induced early development of exodermal Casparian bands and suberin lamellae. In addition to suberization, early lignification of walls of densely packed sclerenchyma cells was found closer to root apex in stagnantly grown plants. Supporting these findings, biochemical analyses revealed that, when grown in stagnant solution, the amounts suberin and lignin in the OPR of all investigated zones were several folds greater than those of plants grown in aerated solution. Similarly, the highest rates of radial oxygen loss from plants grown in deoxygenated conditions were observed just behind the apex and decreased dramatically towards the base. By contrast, ROL from adventitious roots of plants grown in aerated solution was the highest at 30 mm from the apex. A new perfusion technique has been developed to measure the oxygen permeability coefficient of the outer part of root (OPR) of rice. Perfusion of aerenchyma of root segments with mixtures of O2/N2 of known oxygen concentration and at the same time measuring radial losses of oxygen allowed quantification of the permeability coefficient of the cell layers exterior to aerenchyma. The new method for measuring the O2 permeability of the outer part of roots (POPR) was applied to rice grown in either aerated or deoxygenated conditions. The results showed that POPR decreased along the root of plants grown in both conditions. However, when grown in deoxygenated medium, the O2 permeability across the OPR was lower by an order of magnitude at all tested distances compared with plants grown in aerated solution. The lower POPR in roots grown in stagnant solution as well as the reduction of POPR along the roots of plants from both conditions strongly correlated with the development of apoplastic barriers in the OPR. In order to estimate the contribution of apoplast and living cell for the overall movement of O2 across the OPR, the POPR was affected either by blocking the apoplastic pores in the OPR with salt precipitates or by killing the living cells with 0.1 N HCl. Treatment with CuSO4/K4Fe(CN)6 resulted in formation of brown precipitates only in roots of plants grown in aerated solution. This is strong evidence that well-developed apoplastic barriers impeded ion movement across the OPR in these plants. As a result of the formation of salt precipitates in the apoplastic pores of roots grown in aerated solution, the POPR decreased by 20-5%. This is in agreement with earlier findings of diffusional and bulk water flow of Ranathunge et al. (2005). The blockage of the apoplast with precipitates reduced the diffusional water permeability by about 20% and caused a massive 3- to 4- fold reduction of hydraulic conductivity. This suggested that the OPR of rice allow rather high water flow in the presence of relatively high resistance to O2. Killing of root segments by 0.1 N HCl increased the POPR by 20-55% of plants grown in both conditions. At least in part, these increases may result from vanishing the respiratory activity in the OPR. Overall, the physical resistance plays a dominant role in impeding O2 loss from rice roots, although effects due to respiration may contribute, namely, in the presence of low rates of radial oxygen loss. 2. The hydraulic properties in developing grape berries cv. Shiraz and Chardonnay Berries of Vitis vinifera cv. Shiraz can undergo weight loss during later stages of ripening. It was hypothesized that the reduction in net vascular flow of water into the berry, concomitant with transpirational loss, leads to berry weight loss. There may be also some back flow of water from the berry to the parent plant along the xylem. The present study provided first data on the hydraulic properties of the pedicel and components of the berries during development. Comparisons were made between Shiraz and Chardonnay, which is not known to undergo substantial weight loss. It was shown that the hydraulic conductance of single berries of both varieties declined during development. However, Shiraz berries had higher hydraulic conductance than Chardonnay for whole berries and all cut positions. The increase in hydraulic resistance was found in the proximal (brush) region and distal part of the berry, which was much larger in Chardonnay. For Shiraz, the increase in resistance was about half of that observed in Chardonnay. There was no evidence for changes in resistance in the pedicel or receptacle region of the berry. The reduction of hydraulic conductance could be due to combination of both: reduced aquaporin activity in the xylem parenchyma and restrictions in the xylem vessels.