Elongation and Gravireactivity of Roots from an Agravitropic Maize Mutant: Implications of Growth Inhibitors

Growth of agravitropic (AGT) mutant (c.v. Kys) maize roots was significantly higher in comparison to that of two normal gravitropic cultivar roots. Vertical halfdecapitated roots bent towards the remaining half tip. This result can be explained by the fact that cap cells produced growth inhibitors (GI) moving in basipetal direction. The curvatures of half-decapitated roots in Kys AGT root were significantly smaller than in normal cultivar root. One essential consequence of this AGT mutation was brought by low GI content inside the extension zon

Effect of the light on adenine nucleotide content of georeacting maize roots

Apical segments from maize roots of LG 11 and Orla 264 varieties georeacted, at least for the first few hours, only in light, while those of the Anjou 210 variety were georeactive both in light and darkness. The energy charge in the apical end of the two light geo-sensitive (LG and Orla) maize roots significantly increased in the light. In contrast, in Anjou root tips, the energy charge was already high in the dark and did not change significantly after light exposure. The time course of light-induced changes in adenine nucleotide contents in root tips was compared with varietal differences in georeactivity in light and darkness. The present data corroborate the hypothesis that a high energy state in the root tip is a prerequisite for the expression of the root reaction to gravit

Root georeaction affected by exo-β-D-(l,3)-glucanase

Two hour pretreatment with exo-β-D-(l,3)-glucanase cause (at a concentration of 0.4 unit/ml) significant stimulation of the georeaction of maize apical root segments, horizontally placed for 7 hr. Implications of this enzyme effect on cell wall extension are discusse

Light and Gravity Effects on Adenine Nucleotide Content and Energy Charge in Maize Roots

Two millimeter apical segments of maize (cv. LG 11) primary roots were analysed in relation to the effects of light and gravity on adenine nucleotide content. Adenosine triphosphate (ATP) content is very sensitive to these stimuli. ATP levels are lower in roots exposed to light than in those kept in the dark. The energy charge (E.C.) decreases markedly after exposure to light and gravity. For the vertical roots E.C. is stable. Present data confirm the fact that light and gravity may act on cell metabolism, modifying the energy requirements. This will be discussed in relation to some hormone action

Viscosimetric determination of cellulase activity: critical analyses

The mode of expression of cellulase activity obtained by viscosimetric measurement is analysed. After testing different types of substrates, it appears that the best one is hydroxyethylcellulose used at a high degree of polymerisation and a high concentration. Comparison of results obtained with cellulases from Trichoderma viride and extracted from Pisum sativum favours the validity of the determination proposed. Possible physiological significance of the measurements of cellulase activity is also discusse

Extensibility and rheology of collenchyma cells: II. Low-pH effect on the extension of collocytes isolated from high- and low-growing material

Low-pH effects were studied on the extension of isolated fresh, methanol-killed and frozen-thawed collocytes. Fresh and frozen-thawed samples responded to low pH. This response decreased with increasing differentiation. A yield stress was found for frozen-thawed samples. The significance of the response during growth and differentiation is discusse

Extensibility and rheology of collenchyma I. Creep relaxation and viscoelasticity of young and senescent cells

The extensibility of collenchyma cells was methodologically analyzed; extensibility (elasticity and plasticity) and rheology of this tissue are discussed. Experimental conditions are described. Rheological data for young and senescent cells were obtained; they were found to be not Boltzmannian. The permanent strain is not viscous, and is larger for young cells than older one

Abscisic acid effect on the DNA microgradients of decapped maize roots

Longitudinal and transversal total DNA gradients were analysed in 42-μm thin sections of maize root tips. The optimum DNA concentration was found in the apex (quiescent centre and meristem). It significantly increased after removal of the root cap, which can be considered an essential source of abscisic acid (ABA). When the caps were taken off and agar blocks containing ABA were immediately placed on the apical cut sections, the total DNA level in the root apex decreased greatly. ABA regulation of cellular and nuclear behaviour is discusse

Effect of abscisic acid on differentiation and ribulose diphosphate carboxylase of chloroplasts

Daucus carota tissues were grown on Murashige-Skoog medium (MS) at different concentrations with abscisic acid (ABA). Seven bands of chloroplast fractions were obtained on a sucrose gradient. At 10−5M, ABA highly increased chlorophyll and protein nitrogen content of medium density chloroplasts. With increasing age of the tissues, the most active chloroplasts according to their 14CO2 fixation were found in smaller numbers. When treated with 10−5 M ABA, 34 day-old tissues cultivated in vitro showed the chloroplast pattern of 110 day-old tissues. The effect of ABA—given to the tissues during a short pretreatment or continuously present in the culture medium—on the ribulose diphosphate carboxylase activity was analysed. It was found that ABA at 10−5 M strongly inhibited 14CO2 fixatio