Hydrogen peroxide-scavenging enzymes impart tolerance to high temperature induced oxidative stress in sugarcane.

Seventy-one genotypes of sugarcane from diverse agro-climatic zones of India viz. peninsular, northwest, north-central and eastern zones, were screened for their tolerance to high temperature stress based on the damage to leaf biomass i.e. necrosis of leaf-tips and margins, and rolling of leaves. Nine selected genotypes showing variable response to heat injury were tested for activity pattern of isoforms of two H2O2-scavenging enzymes; ascorbate peroxidase (APX) and catalase (CAT), under high temperature induced oxidative stress. Changes in the activity of APX and CAT isozymes in leaves corresponded to the level of tolerance of genotypes towards heat injury which was substantiated by the highly negative correlation coefficients of heat injury levels of leaves vs. integrated density of APX and CAT isozyme bands. This indicated that the criteria of higher expression of CATs’ and APXs’, the two major reactive oxygen species scavenging proteins in leaves may be used to screen large seedling populations and germplasm for high temperature tolerance.

In-situ monitoring of chromium cytotoxicity in sugarcane.

The potential of in-situ monitoring of cytotoxic effects of chromium through root-tip assay was studied in a sugarcane cultivar CoLk 8102 (Saccharum spp. hybrid). Sugarcane setts supplied with graded concentrations of chromium (VI), exhibited a reduction of 85.92 and 95.10 % in mean root length at 40 and 80 ppm Cr dosages along with 61.25 and 82.50 % reduction in mean root number/node respectively. Mitotic index of root tip cells of treated setts declined and the frequency of aberrant mitotic phases increased pari passu to the increasing chromium concentration. To compare and quantify the effect of graded chromium dosages on frequency of chromosome aberrations vis-à-vis inhibition of mitotic activity, a ‘Decretion factor’ (D.F.) has been used for the first time. The value of DF increased with the increase in the chromium dosages. The increase in chromosome aberration frequency was low at low chromium dosages (1 or 2 ppm), but the high Cr dosages (40 and 80 ppm), induced sharp reduction in mitotic efficiency of root system along with anomalies in the process of cell division and induced chromosome aberrations in sugarcane root meristem, which in turn affected the over all plant growth.

Effect of distillery spent wash on cytomorphological behaviour of sugarcane settlings.

Characteristics of crude and digested spent wash (distillery waste), and effect of their application on cyto-morphological attributes of settlings of eleven genotypes of sugarcane (Saccharum species hybrids) were studied. High concentrations of K, P, S, Fe, Mn, Zn and Cu contents and heavy metals were present in crude spent wash as compared to the digested one. Root meristem assay of settlings grown on crude and digested spent wash showed a detrimental effect on mitotic efficiency and also induction of de novo chromosomal aberrations viz. clump formation, chromosome stickiness, laggards and micronuclei formation etc. higher number of chromosomal abnormalities as compared to those of control conditions. Mitotic index of root-meristems of different genotypes showed a decline of 62.65 to 100% in crude spent wash treatment and 36.94 to 90.33% decline in digested spent wash treatments as compared to the control. However, an improvement to the extent of 27.73% was observed in the mitotic activity of root-meristems treated with diluted spent wash (1:5 v/V with water). Inhibitory effects of digested and crude spent wash were also visible on bud sprouting and settling height, but 1:5 aqueous dilution of spent wash stimulated the early growth attributes. Such beneficial effects of diluted spent wash were observed in most of the sugarcane genotypes.

A simple parameter of dispersion index that serves as an adjunct to karyotype asymmetry.

In order to refine the measure of karyotype asymmetry a new chromosomal parameter of dispersion index is proposed that has the potential to decipher even the minor karyotypic variations, thus permitting further evolutionary gradations to the karyotype asymmetry classes of Stebbins. The higher the dispersion index, the more specialized would be the karyotype. The dispersion index takes into account the variance lor gradual change in chromosome size within a complement vis-a-vis variance for the position of centromere in a karyotypic totality. The dispersion index is calculated as the proportionate measure of centromeric gradient to the coefficient of variation for chromosome length; wherin centromeric gradient = length of median short arm – length of median chromosome. Thus, the three most important karyotypic criteria viz., differences in: absolute chromosome size, position of centromere and relative chromosome size, are all covered in the proposed parameter. The effectiveness of dispersion index has been tested on a plant taxa, Papaver L., where karyomorphological details, nuclear DNA content, and morphotaxonomic parameters have been amply elucidated from an evolutionary stand point. It is hoped that dispersion index would find immense utility in delimiting species interrelationships particularly in the closely related taxa, when applied in conjunction with other systematic parameters.