Effects of storage conditions on chlorophyll content in diploid black wattle (Acacia mearnsii)

Abstract

Black wattle (Acacia mearnsii de Wild) is a commercially important forestry species in South Africa, however, being an exotic it is also seen as an invader of indigenous vegetation. Research into producing a sterile variety is underway and one such route being explored is the production of a polyploidy. Within this research it is critical to have reliable and affordable methods to identify the polyploids from the normal diploid material, one such method identified is using chlorophyll content. A practical limitation of this method is that many of the samples being tested are in the field and away from the laboratory and thus research has been aimed at storage of the samples as a means to preserve the chlorophyll prior to absorption spectral analyses. The effects of storage of leaves on chlorophyll content were determined in five non-identical two yearold nursery diploid black wattle genotypes. Fifteen leaf samples from each genotype were either oven dried and then stored for one week or one month at room temperature, or frozen for one week or one month at -4°C, before chlorophyll was extracted and absorbance spectra determined. Chlorophyll absorbance values were assessed at three peaks, namely, 433 nm, 456 nm and 663 nm. Chlorophyll extracted from leaf material on the day of collection (day-0) was used as the control. Assessment of the total mean chlorophyll absorbance (TA), sum of the three peak absorbance mean values (), revealed significant differences between all treatments (p < 0.01) as well as significant differences (p < 0.01) from the control (T = 1.275). Chlorophyll absorbance values within dried and frozen treatments were compared with respect to storage time periods of seven days and 28 days. Dried leaves that were stored for seven days (T = 1.132) resulted in the least amount of chlorophyll degradation followed by 28 days ice storage (T = 1.114), seven day ice storage (T = 1.103) and lastly 28 days dried storage (T = 1.093). Analysis of variance revealed that within individual plants, the chlorophyll absorbance values between wavelengths, were significantly different (p< 0.05). It was noted that whilst all treatments decreased from the control (day-0), dried samples decreased steadily over time whereas a similar trend for frozen samples could not be identified.

Keywords: chlorophyll absorbance, dry storage, ice storage, polyploidy

Southern African Forestry Journal Vol. 207 2006: 21-26