Agriculture Reference
In-Depth Information
et al.
2009
). Especially among the micronutrients, including REDOX-active
transition metals such as copper or zinc, the concentration range between deficiency
and toxicity is often narrow, both having negative effects on plant growth
(He et al.
2005
).
Plants are able to respond flexibly to varied environmental conditions. In
addition to light, water and temperature, mineral nutrient availability determines
plant growth and propagation, or, in an agricultural context, crop yield. The
ecological niche of a plant is determined by the specific range of conditions a
certain plant species can adapt to. Crop cultivars are usually the result of adapted
breeding for agricultural conditions and, as a result of this selection process, they
are disposed to narrow genome variability (Tanksley and McCouch
1997
). There
are different avenues to re-introduce increased genetic variability, but all
approaches have to take into account the need to retain the very high yield potential
of modern crop cultivars, otherwise the necessary goal of sustainably and afford-
ably providing more food for a growing population on less land will not be met.
Mineral nutrient deficiencies typically result in yield depression and quality
impairment in crop plants. Here we compare what is known about the effects of
mineral depletion on plant development and metabolic composition to natural
developmental senescence of plants. The model plant
Arabidopsis thaliana
pro-
vides all the necessary tools to perform such studies at a systems biology level. The
conclusions from such investigations will be helpful for developing concepts for
breeding of nutrient use efficient crops and will provide directives for more
sustainable agricultural practice.
Senescence - A Developmentally Controlled Process Critical
for Seed Development
Leaf and whole plant senescence is a genetically programmed and highly regulated
process termed developmental senescence (Wu et al.
2012
; Thomas
2013
;
Watanabe et al.
2013
). This is essentially a self-destructive programme, which
directs breakdown of cellular structures and components in source tissues for export
to sink tissues such as young leaves, roots, flowers, tubers or seeds.
The developmental cycle of an annual plant (Fig.
8.1
) starts with germination
and a growth phase leading to leaf expansion, during which young leaves act as a
sink for carbohydrates and root-derived mineral ions. This is followed by a phase of
maturity, in which fully expanded leaves are photosynthetically and biochemically
most active and provide metabolites to developing leaves or other sink tissues such
as roots and developing seeds. Older leaves successively senesce, but after anthesis
and fertilisation, developing seeds act as the major sink and the plant is primed for
general senescence. Upon the switch from vegetative to generative growth, no new
leaves develop and existing leaves enter senescence to provide nutrients to the
seeds. During this phase the plant has to find a compromise between degradation of
macromolecules to remobilise nutrients and leaf functional integrity for photosyn-
thesis and carbohydrate production. For example in rice, wheat and barley, up to
