Root system morphology and anatomy of cold-sensitive Penjalinan and cold-tolerant Z 7 genotypes of maize

Growth, morphology and anatomy of seminal roots (primary and adventitious), mesocotyl and nodal roots (1st node) were analyzed in 16-day-old seedlings of cold-sensitive Penjalinan and cold-tolerant Z 7 maize genotypes that had been exposed to 7 day period of 24 degrees C (control) or 6 degrees C (chilling stress) temperatures. Quantitative differences between the untreated genotypes included less abundant or absent adventitious seminal roots, more numerous mesocotyl and nodal roots, and a higher root branching density in the tolerant Z 7 plants. At anatomical level, the area of root, stele, cortex, and the total xylem conducting area were larger in cross sections of primary and mesocotyl roots but smaller in the adventitious seminal and nodal roots of the tolerant Z 7 plants compared to the sensitive Penjalinan plants. Chilling caused growth inhibition of the main root axes. Number and total length of lateral roots decreased in both genotypes. At anatomical level, the root tissues were not affected in the earlier developed primary, adventitious seminal, or mesocotyl roots. Chilling inhibited initiation and growth of the nodal roots in which smaller area of the tissues, a lower proportion of conducting area and consequently lower conductive capacity developed during stress period. Decrease in dry matter of the whole root system was observed. The effects of chilling were more pronounced in the sensitive Penjalinan genotype. The chilling tolerance of the Z7 genotype corresponded with both higher capability of dry matter production, anatomical properties and conductive capacity of the mature primary root (dominant during early stages of maize development), and with less severe inhibition of growth and development of vascular tissues in the nodal roots (that would become fully active in later ontogenetical stages).