Phytic acid prevents oxidative stress in seeds : evidence from a maize (Zea mays L.) low phytic acid mutant

A maize mutant defective in the synthesis of phytic acid during seed maturation was used as a tool to study the consequences of the lack of this important reserve substance on seed survival. Data on germinability, free iron level, free radical relative abundance, protein carbonylation level, damage to DNA, degree of lipid peroxidation, \u3b1- and \u3b3-tocopherol amount and antioxidant capacity were recorded on seeds of maize B73 and of an isogenic low phytic acid mutant (lpa1-241), either unaged or incubated for 7 d in accelerated ageing conditions (46\ub0C and 100% relative humidity). The lpa1-241 mutant, compared to wild type (wt), showed a lower germination capacity, which decreased further after accelerated ageing. Whole lpa1-241 mutant kernels contained about 50% more free or weakly bound iron than wt ones and showed a higher content of free radicals, mainly concentrated in embryos; in addition, upon accelerated ageing, lpa1-241 seed proteins were more carbonylated and DNA was more damaged, whereas lipids did not appear to be more peroxidated, but the \u3b3-tocopherol content was decreased by about 50%. These findings can be interpreted in terms of previously reported but never proven antioxidant activity of phytic acid through iron complexation. Therefore, a novel role in plant seed physiology can be assigned to phytic acid, that is, protection against oxidative stress during the seed's life span. As in maize kernels the greater part of phytic acid (and thus of metal ions) is concentrated in the embryo, its antioxidant action may be of particular relevance in this crop

Structure and dynamics of flour by solid state NMR: effects of hydration and wheat aging

The effects of accelerated aging of wheat seeds on structural and dynamic properties of dry and hydrated (ca 10 wt % H2O) flour at a molecular level were investigated by several high and low resolution solid-state NMR techniques. Identification and characterization of domains with different mobility was performed by 13C direct excitation (DE) and cross-polarization (CP) magic angle spinning (MAS), as well as by 1H static and MAS experiments. 1H spin-lattice relaxation times (T1 and T1F) measurements were carried out to investigate molecular motions in different frequency ranges. Experimental data show that the main components of flour (starch and gluten proteins) are in a glassy phase, whereas the mobile fraction is constituted by lipids and, in hydrated samples, absorbed water. A lower proportion of rigid domains, as well as an increased dynamics of all flour components are observed after both seeds aging and flour hydration. Linear average dimensions between 20 and 200 Å are estimated for water domains in hydrated samples

Plasma-membrane proteins in water-stressed sunflower seedlings

In sunflower seedlings either regularly watered or subjected to water stress by withholding water for 5 days, plasma membrane was isolated by partitioning in an aqueous polymer two-phase system. In the stressed seedlings an osmotic adjustment of 0.1 MPa took place. Water deficit conditions determined an increase in membrane permeability and in the recovery of plasma membrane proteins. Total and soluble protein levels decreased by 9.4 and 45.8% respectively in the stressed seedlings. The sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the soluble proteins and plama membrane proteins did not show qualitative changes in the protein patterns of both the control and the stressed seedlings. Several quantitative differences in the levels of plasma membrane proteins were observed: the 60, 56 and 37 KDa bands, as well as the 37 to 20.1 KDa group, reached higher levels under stress. These last polypeptides can be identified as peripheral plasma membrane proteins of the bilayer