Rapid microwave processing of winter cereals for histology allows identification of separate zones of freezing injury in the crown
In histological studies, microwave processing of tissue considerably shortens the time required to prepare samples for observation under light and electron microscopy. However, plant tissues from different species and different regions of the plant respond differently to microwave processing, making it impossible to use a single protocol for all plant tissue. The crown of winter cereals such as rye (Secale cereale L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and oats (Avena sativa L.) is the below-ground portion of the stem that overwinters. It is composed of numerous types of cells with an organizational pattern that is similar to other grasses. When we used microwave protocols that were developed for other plant tissues, winter cereal crown tissue shattered and crumbled when sectioned. This study reports a procedure developed to process winter cereal crowns for histological observations. Using this microwave protocol, samples were prepared in 1 d as compared to 2 wk using traditional protocols. This enabled many more samples to be processed and allowed us to identify four overlapping zones of response to freezing within the crown. Results of varying time, temperature, and microwave wattage during fixing, dehydrating, and embedding in paraffin are described. High quality sections from the crowns of oat, barley, wheat, and rye indicate that this procedure is valid for all winter cereals. Since crown tissue is similar across all grass species, we predict that the protocol will be useful for other grasses as well.