Techniques for detecting and measuring developmental and maturational changes in tuber native periderm

Abstract

We developed a technique to quantitate native periderm permeability during tuber growth and maturation by porometrically determining vapor conductances. We also describe a simple, inexpensive means of determining the corresponding weight per unit area of suberized phellem cells (skin) in native periderm during tuber growth and maturation as a means of assessing the developmental status of native periderm. The porometric technique is very sensitive and rapid. Porometrically derived vapor conductances of mature native periderms were measured without difficulty, and native periderms were found to release ~0.005 moles of water vapor/meter2 native periderm surface/sec. into a dry test atmosphere. Immature native periderm released up to 28 times more water vapor than mature periderm even though the phellem cells were histochemically determined to possess both major components of suberin. We demonstrated use of the porometric technique by determining maturational changes in periderm permeability of growing/immature tubers and mature tubers at harvest. The technique revealed that the native periderm of Russet Burbank tubers was more permeable and had the potential to lose more water vapor, until becoming permeably mature, than Norchip or Norland tubers harvested on the same dates. The dry weight of the skin (phellem tissue) of native periderm (mg/ cm2) for all three cultivars increased during tuber growth, but plateaued to a relatively constant level, or slightly declined, while plants were still alive during the latter period of tuber growth. During this period, periderm vameable conductances were undergoing substantial declines. Comparison of skin dry weights of immature tubers indicated that stem end regions of tubers were developmentally ahead of equatorial and bud end regions; this difference decreased as the tubers matured at harvest time and was less apparent with some cultivars.