EFFECT OF SALINITY AND EXOGENOUSLY APPLIED POLYAMINES ON GROWTH AND ION RELATIONS IN SPINACH

ABSTRACT

It has been suggested that polyamines are involved in many growth and development processes in plants and may serve as growth regulators. These nitrogenous compounds have been shown to be involved in cell division, nucleic acid and proteins synthesis, and normal senescence. It is thought by some that polyamines may be involved in the plant's mechanistic response to stress. More importantly, some reports indicate that exogenously applied polyamines can overcome the growth reduction brought about by salinity stress. In this report, growth studies were performed on to examine the effect of exogenously applied putrescine, spermidine, and spermine on the alleviation of salinity stress. Spinacia oleracea, L. cv. Space was chosen since much of our understanding of the sugar metabolism needed for growth has been derived from this plant. Polyamines were applied in a manner used in earlier reports, i.e., foliar spray. The effect of salinity and polyamines on leaf number, leaf area, fresh and dry weight was observed. Our analysis showed that putrescine and spermine had no significant effect on plant growth throughout the range of salinities studied (2 to 11.7 dS m⁻¹). Spermidine slightly decreased growth. Further studies on ion uptake indicated that none of the polyamines tested had a significant effect on plant ion content. While we failed to document any growth response to putrescine or spermine treatment, we did find a significant reduction of growth as salinity increased in the irrigation water. Further analysis of the ion data indicated that K⁺:Na⁺ selectivity significantly increased with increasing salinity. This preferential increased influx of K⁺ ions may be an important mechanism by which spinach maintains low Na⁺ tissue levels relative to external concentrations. Additionally, Ca²⁺:Na⁺ selectivity as measured by the Gapon constant, K _g , greatly increased. Conversely, Ca²⁺:Mg²⁺ selectivity decreased resulting in an increase in Mg²⁺ tissue concentrations. Our results are discussed in terms of possible salt tolerance mechanisms in spinach as they relate to the preferential uptake of specific nutrient ions from saline irrigation waters.

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