Influence of Potassium Deficiency and Temporary Potassium Deficiency on Nitrogen Metabolism in Leaves and Berries of Wine Grapes

During the 1991 season work was conducted to develop a procedure for putrescine estimation that could be performed quickly with simple equipment. Since the putrescine level increases many fold in leaves affected by potassium deficiency, it seemed likely that a simple procedure could be developed for the rapid diagnosis of potassium deficiency even when symptoms are mild or not yet visible. We have been successful in developing a rapid screening procedure to evaluate putrescine in dried and fresh grape leaves; this method is also applicable to petiole and rachis tissue. We found that making a derivative of putrescine using 5-dimethylaminonapthalene-l-sulfonyl chloride (Dns-Cl) gave a compound that was highly florescent and could be readily separated from other amine derivatives by TLC. We have now optimized the conditions and volumes used for the assay so that putrescine in the normal range in just barely visible under the conditions of the assay. This means that samples with elevated putrescine show large florescent spots and are easily distinguishable from the samples with normal levels. The previously used HPLC procedure could only accommodate 6 to 8 samples per day and running the instrument was rate limiting. With the new procedure we can easily screen 60 to 80 samples in a single day and grinding the samples is now the rate limiting step in the operation. We have therefore increased throughput by an order of magnitude and with this capability we now feel that the survey work to characterize putrescine and potassium levels in California vineyards can now be carried out.