SPERMIDINE PRETREATMENT OR ROOT-TIP REMOVAL IN MAIZE SEEDLINGS - EFFECTS ON K plus UPTAKE AND TISSUE MODIFICATIONS

Three-day-old maize seedlings were transferred to fresh growth solution with or without spermidine (Spd), or had the primary root tip removed and were then transferred to fresh growth solution. Spd pretreatment resulted in 50 % inhibition of root extension in intact plants after 24 h, while no growth was detected in tipless roots. After 18 h of either treatment, K+ uptake measurements taken from subapical segments of freshly cut roots (T(o)) showed values higher than those obtained in freshly cut segments from control seedlings. The values were similar to those from washed control segments. Moreover, the roots from seedlings exposed to Spd pretreatment showed an increase in polyamine oxidase (PAO) and peroxidase (POD) activities. An earlier differentiation of xylem tissues and a stronger autofluorescence of vascular parenchyma, xylem vessels and rhizodermis were detectable in Spd-pretreated roots as compared with control roots. The same phenomena, except for the autofluorescence of vascular parenchyma, were observed in tipless roots. The reported effects suggest that both Spd pretreatment and tip removal induce a stress that may result in early differentiation, making roots less sensitive to the inhibiting effect of cutting injury on K+ uptake.