competition between beneficial and pathogenic microbes

These microbes can almost be viewed as an extension of the plant into the soil. Like the human gut microbiome

Metagenomics allows species to be sequenced from soil samples without culturing, largely overcoming this bottleneck.

Flavonoids are a group of phenolics that can be specifically exuded into the rhizosphere as signal molecules to attract rhizobia

Rhizosphere acidification affects nutrient acquisition by liberating cations from negative adsorption sites on clay surfaces and solubilising phosphate from phosphate-fixing soils.

Enzymes are also released from roots, particularly phosphatases, which cleave inorganic phosphate from organic sources

Barber and Martin (1976) showed that 7–13% of net photosynthate was released by wheat roots over three weeks under sterile conditions while 18–25% was released when roots were not sterile. This difference might be considered carbon released because of microbially-induced demand in the rhizosphere, and therefore made unavailable for plant growth.

rhizosphere

kilometres of new roots each year

Wheat, a monocot, has a dual root system. Seminal roots emerge from the seed and nodal roots (thicker roots on the outside of the picture) emerge from the crown, a group of closely packed nodes from which tillers emerge.

mass flow is driven by plant transpiration and is the movement of soil solution along a water potential gradient.

Na (for many sea-shore plants).

Efficient root growth is also an important factor in maximising yield with lower fertiliser applications because ‘wasted’ root growth costs energy that could otherwise be invested in the crop of interest

Over long periods, sucrose is taken up slowly but permeability relative to water is negligible.

Turgor changes also change the curvature of hairs of insectivorous plants. In the case of the Venus fly trap, sensory hairs coupled to an electrical signalling system require stimulation at least twice within a 30 s period

This occurs because nutrient uptake is an active process, independent of water uptake from the soil, and continues during the night – the rate of nutrient uptake varies little over 24 h.

The Casparian strip and the suberisation of the endodermis is important as it provides a barrier to prevent back-flow of water and also structural support so that the root can contain a positive pressure at night.

The distribution of water in the different pathways depends not only on the age of the root, but may also vary with the flux of water moving through, that is, the rate of transpiration.

the Casparian strip in the primary wall prevents flow of water and solutes through the wall from inner cortex to stele

Figure 3.47.

whole length of a leaf blade while small veins and their transverse connections distribute water locally, drawing it from the large veins

A rapidly transpiring leaf can evaporate its own fresh weight of water in 10 to 20 min, though many plants such as cacti, mangroves and plants in deep shade have much smaller rates of water turnover

move water to the canopy at rates that satisfy the transpirational water loss at the leaf surface.

The concentrations also vary at different times of day, being lowest in the middle of the day when transpiration is highest, and quite high at night when stomates are closed so there is very little flow of sap to the shoots.

When the vessels mature, and their end walls disintegrate, their cellular contents are carried away by the transpiration stream.

allows plants to move large quantities of water from the soil to the transpiring leaf surface with little input of metabolic energy

hydrostatic pressure falls by 10 kPa for each metre increase in height

Figure 3.9.

Water will flow from a sample with a high water potential to one with a low water potential

1 MPa applied over 100 cm2 is equivalent to a weight of one tonne

The ratio of water lost to CO2 taken up is around 300:1 in most land plants

Water loss also has a benefit in maintaining the leaf temperature through evaporative cooling

a large tree may transpire hundreds of litres of water in a day.

The nature of this ‘CO2 pump’ and the energetics of carbon assimilation are not fully characterised in SAM plants but considerable CO2 concentrations do build up within leaves, enhancing assimilation and suppressing photorespiration.

CAM species outnumbering C4 species by about two to one

The biomass production per unit water utilized in CAM was 6 times higher than for C3 plants and 2 times higher than for C4 plants when plants exhibiting all three photosynthetic pathways were grown together in a garden outdoors (Winter et al. 2005).

C3-C4 photosynthesis does not improve photosynthetic efficiency

The inter-connecting cytoplasm between the two intra-cellular compartments

CO2 assimilation by all three C4 subtypes

Figure 2.7.

maximum photosynthetic rates were double twentieth century values

include several important food crops such as maize and sugarcane

Rubisco first evolved when the earth’s atmosphere was rich in CO2, but virtually devoid of O2

On a global scale, this investment equates to around 10 kg of nitrogen per person!

Figure 2.2

fructose-1,6-bisphosphate

PCR

UV is dissipated harmlessly, lowering quantum yield compared  with growth-chamber plants

the Chl a/b ratio will be lower compared with that in strong light

Quantum yield is reduced as a consequence, and leads to a slight discrepancy between in vivo absorption maxima (Figure 1.8) and quantum yield

Fluorescence induction kinetics

the solution will appear deep red due to energy re-emitted as fluorescence

If the chloroplasts, still in the dark, are rapidly transferred to a pH 8.0 buffer containing ADP and Pi, ATP synthesis then occurs.

A massive ΔpH, of approximately 3–4 pH units, equivalent to an H+ ion concentration difference of three to four orders of magnitude

four basic complexes

commonly 200–300 in each palisade cell

both quantum yield and light-saturated plateaux depend on CO2 concentration

quantum yield expressed in terms of incident irradiance does not necessarily reflect the photosynthetic efficiency

sensitivity of a leaf to these variables is not fixed but can change over time in response to, for example, drought.

light profile

pre-eminent

Irregular-shaped cells in spongy tissues enhance scattering, increasing the path length of light

photosynthetic processes

Figure 1.1 A

genotype x environment interactions

roots

If the loop was not complete, the structures that comprise it would not exist.

Plants