Early effects of boron deficiency on membrane function in higher plants

Thesis



The transfer of plants to boron-free solutions induces rapid responses in membrane functions without necessarily affecting root growth and anatomy. In sunflowers (Helianthus annuus), root growth slows within 3-6 h. However in maize (Zea mays), no growth effects are apparent after more than 30 h without boron (-B). In both species early disturbances in ion uptake and cell wall deposition are seen.

Ultrastructural studies on sunflower root tips after 5.5 h or 3 d -B are reported. Detailed studies on the absorption of P_j and K⁺ by root tips were complemented by studies on protoplasts isolated from the root tips of +B and -B plants. There were no significant differences in the protoplast yield or viability according to their B status. Ion absorption by protoplasts isolated from roots of +B and -B plants generally resembled that by intact roots of the corresponding B status.

Altering the B status of the protoplasts was expected to initiate earlier responses than in the roots where cell wall binding and diffusion times buffer the system against change; but the greater variability inherent in measuring the protoplast responses prevented the detection of subtle changes.

The activities of two+ membrane bound arjzymes were investigated; β-glucan synthetase and a K⁺-stimulated, Mg²⁺ -dependent ATPase. UDPG incorporation by protoplasts continued for over 18 h and was consistently higher in +B protoplasts and root membranes than -B. However SEM revealed no significant differences in fibre deposition around sunflower and maize protoplasts according to their boron status.

(K⁺+Mg²⁺)-ATPase from sunflower roots was found to be reversibly impaired by the loss of B; and preliminary investigations implied that restoration of activity when B was resupplied to the intact roots was correlated with the B content of the membrane fraction, as determined by the (n,α) method.

Authors: Heyes, J; Julian Andrew Heyes

• Publication date: 1984
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Boron; Growth (Plants); Plant membranes