ENGLISH VERSION

ZESZYT 356

Grzegorz Łysiak
Deformations of wheat caryopsis endosperm caused by moisture loss

Introduction. The endosperm of wheat caryopsis under the influence of moisture and temperature gradients, which occur during growing, as well as during harvest and storage undergoes characteristic internal damages. However, any interpretation of the mechanisms of initiation and developing of such damages is still not available. It is reasoned from the complex kernel geometry, its nonhomogenous structure, and changing kernel properties in relation to the vast number of factors. The analyses taken in the study focused on the influence of water content upon properties of wheat caryopsis, and mainly on its geometrical features.
Origin and aim. The aim of study was analysis of deformations and strains of wheat caryopsis endosperm as the result of moisture loss. Discovering of relationships in this field could help for a better understanding of the causes and mechanisms of wheat fissuring phenomenon.
Material and methods. The research was done on mature wheat kernels of six varieties i.e. ‘Kobra’, ‘Flair’, ‘Bombona’, ‘Raweta’, ‘Hewilla’, and ‘Monsun’ as well as immature kernels of one variety ‘Turnia’. The caryopses were dissected in transverse and longitudinal planes, soaked in water, and after introducing a marker agent on their surface, dried in ambient conditions. The changes of geometrical features of endosperm caused by moisture loss were observed with a help of stereoscopic microscope SMT-800, and successively registered in form of digital images using Nicon Coolpix 4500 digital camera. Image analysis of the obtained images was done with a help of ImageExpress software. Influence of drying time upon strains of endosperm in three directions, i.e. along kernel width, thickness, and length was determined. The detailed analysis included comparisons of strains  for selected sub-regions of endosperm, i.e. whole cross-section, its ventral and dorsal parts as well as for individual cheeks. The contour maps of endosperm deformations in transverse and longitudinal cross sections were generated.
Results. Wheat caryopsis has undergone significant strains as the result of drying. The fastest changes were observed already at the first minutes of the process. The strains in relation to the moisture contents of dried kernels were the best described by second degree polynomial equations. The results of comparisons of strains along caryopsis width, thickness, and length discovered the significant differences between the averages. The highest values of strains occurred at the ventral side of wheat caryopsis in direction of its width. Along length of the kernel strains were significantly lower, they were both compressive and tensile. It was noticed that moisture loss caused a crease opening effect being the result of endosperm shrinking and relative displacement of the opposite cheeks. The contours maps generated in the transverse cross section of wheat caryopsis uncovered differences in deformations which occurred between ventral and dorsal kernel sides. For the longitudinal cross section the obtained contour maps confirmed large, local differences in endosperm deformations reflecting the process of developing of transverse, internal cracks. The results obtained for immature caryopses showed to be similar for those obtained for the mature ones.
Discussion. The results of experimental part of the study were discussed with close available in subject literature. The lack of similar and important studies was underlined in. Some original observations concerning the manner of caryopsis deformation as well as the resulting strain state not evoked in literature were underlined. On the basis of the discovered relative differences between strains with respect to direction an explanation of the transverse kernel cracking phenomenon was proposed. The meaning of the study results as well as a need for continuous research in some relative filed areas was discussed, like the meaning of endosperm heterogeneity for mechanical analyses of its properties, and need for more profound analysis of some changing kernel geometry features in view of wheat breeding and processing optimization. 
Conclusions. The undertaken study has discovered, that wheat caryopsis reacts in a dynamic way to the changing moisture conditions. The dried caryopsis undergone both changes in dimensions and shape, and resulted in different strains accompanied by successive endosperm cracking. It was noticed that the obtained sketch of endosperm deformations and its strain state well reflects frequently observed kernel fissures. The significant shrinkage of wheat caryopsis in its transverse cross section is not followed by such intense reaction along its length. Hence, the caryopsis shrinks mainly peripherally with only little change in length. Corresponding to the deformations generated internal forces may be concentrated on the regular, transverse arrangement of tissues. It can cause the effect of stress concentration and increase of tensile stress along kernel. It was discovered that locally large deformations of endosperm can arise long before the kernel mature state as the result of moisture loss during caryopsis development.