The biology of Molinia caerulea (L.) moench with special reference to population variation.
Molinia caerulea, the purple moor grass is widely distributed
and morphologically variable. Its occurrence on well-drained Ca'+-rich
alkaline Leblanc waste is unusual since the grass normally has a
calcifuge habit and grows an wet acid peaty soils. Molinia is deciduous
losing its leaves after the formation of an abscission zone. Leaf
abscission in grasses is rare.
This project aims, therefore, (a) to investigate the anatomy
of leaf abscission in Molinia using scanning electron microscopy;
(b) to quantify and explain morphological and biochemical differences
which occur between two populations growing in contrasting habitats,
namely acid moorland and Leblanc waste.
Scanning electron microscopy of freeze fractured nodes of naturally
senescing Molinia showed that leaf separation was due to separation
of cells along the middle lamella, although some cells showed fractured
cell walls. Molinia should prove an interesting model in which
to study abscission process in the Gramineae.
A comparative study of the two contrasting populations of Molinia
was made. Twenty-four morphological characters were used to classify
the Molinia. Multivariate analysis distinguished the two populations.
Acid-moorland plants were characterised predominantly by vegetative
features eg. leaf length, plant height. Whereas in alkaline-waste
Molinia, flower morphology was most important eg. culm length, lemma
length. There were differences in growth and flowering between
the two populations. Differences in growth were maintained under
constant conditions suggesting that endogenous factors were responsible.
Classification using cluster analysis of proteins extracted
from basal internodes separated by SDS-PAGE distinguished between
the two populations. Analysis of isoenzyme patterns obtained from
SGE and PAGE showed that variation within each population was greater
than that between populations. There was thus no evidence of genetic
differences between the two populations.
Root-surface phosphatase activity of both field and laboratorygrown
plants showed pH optima appropriate to the field environment
of the roots. In laboratory grown plants, there was evidence that
the enzyme activity responded to changes in pH but not calcium concentrations.
Variability in Molinia populations involves both endogenous
factors and phenotypically plastic modifications at both whole organism
and molecular levels.