Soft Plant Tissues Research Articles

A Device for Grinding Cereal Crowns

Currently available tissue grinders effectively grind most soft plant tissue such as leaves and stems. However, none of the devices tried in this laboratory would adequately grind fresh cereal crown tissue. A device made from stainless steel and mounted in a commercial hand drill is described. This device will rapidly grind fresh crown tissue and is easily cleaned between samples.

Elastic‐Plastic Constitutive Relations of the Cell Walls of Apple and Potato Parenchyma

The rheological properties of the cell walls of soft plant tissue have a strong bearing on the stress‐strain response of the whole tissue. In this study the parenchyma cells of apple and potato tissue were osmotically manipulated in mannitol solutions, and the cell wall stress‐strain relation was inferred from precise measurements of the change in dimensions of the tissue samples. Cell wall tension was estimated from the water potential of the solutions, cell water relations, and simple shell theory. Cell wall stress versus strain showed an increasing slope with increased strain, but for potato parenchyma, slope decreased when strain exceeded 8%. Samples prestressed at high turgor showed significant irreversible deformation on subsequent plasmolysis. Two new constitutive laws were developed to describe the elastic‐plastic behavior of the cell walls.

Subterminal Polygalacturonase, a Nonmacerating Enzyme, Attacks Pectate from the Reducing End

Subterminal polygalacturonase from Aspergillus, which fails to macerate soft plant tissue in spite of a rapid action on pectate in vitro, was examined for its action at pH 3.5 on substrate (degree of polymerization 9-50) altered by the reduction of the reducing end to (3)H labeled l-galactonic acid, and the introduction of unsaturation in a portion of the nonreducing end groups. Endo-polygalacturonase from Saccharomyces fragilis was used as a control. The hydrolysis products were separated by gel filtration chromatography and the sugar residues, the tritium label, and the ultraviolet absorption (of the unsaturated groups) were measured. Endo-polygalacturonase gave equal production of the two end-labeled oligomers. Subterminal polygalacturonase rapidly produced a mixture of tritiated oligomers (mainly trimer, dimer, and tetramer), 2.5 times faster than it liberated unsaturated oligomers, and 3 times faster than it liberated unlabeled oligomers, showing that its action begins at the reducing end. The unsaturated pentamer and hexamer, which accumulated during the rapid phase of enzyme action, were subsequently hydrolyzed to the unsaturated tetramer, in accord with action from the reducing end.