Higher Plant Respiration and Its Relationships to Photosynthesis
79
of metabolism. In support of this generalization, it is commonly observed
that the rate of plant respiration displays a stoichiometric relationship with
the rates of, e.g., growth, translocation, nutrient uptake, and nitrogen
assimilation (Farrar 1985; Amthor 1993b).
4.2.4 Respiration Rate and Carbohydrate Level
A strong positive correlation often exists between plant or tissue carbohydrate content and respiration rate, suggesting that carbohydrate level and
respiration rate are related (Williams and Farrar 1990; Farrar and JHH
Williams 1991; Amthor 1993b). Respiration can be under short-term (minutes to hours) control by ADP availability, however, even though it is
correlated with carbohydrate level over the longer term (Journet et al. 1986;
Brouquisse et al. 1991; Douce et al. 1991). Notably, the addition of sugars
to a tissue increases respiration in the short term when that tissue has been
starved or excised from a supply of endogenous sugars, but not usually
otherwise (ap Rees 1988; Rebeille 1988; Williams and Farrar 1990). Moreover, the relationship between carbohydrate level and respiration rate is
often strongest in growing tissues, and may be absent in mature organs, i.e.,
growth respiration appears to be controlled by carbohydrate level but maintenance respiration does not (Am thor 1989).
It has been inferred that carbohydrates induce processes consuming respiratory products so that over the long term (hours to days) respiration is
positively related to carbohydrate level, but through respiratory control
mechanisms (Bingham and Farrar 1988; Farrar and JHH Williams 1991;
Farrar and ML Williams 1991). For example, an increase in (specific) sugars
may stimulate root nitrate uptake and assimilation (Hanisch ten Cate and
Breteler 1981; Aslam and Huffaker 1984) and perhaps enhance cell division
and differentiation (Williams and Farrar 1990; Farrar and JHH Williams
1991). Each of these increase the demand for carbon skeletons and energy.
Protein levels may be regulated by carbohydrate concentration (Baysdorfer
and van der Woude 1988; Wenzler et al. 1989) with a decrease in cellular
carbohydrate level leading to a loss of respiratory machinery (Journet et al.
1986) and an increase in sugars resulting in increased respiratory capacity
(Ave lange et al. 1990; Farrar and JHH Williams 1991). Conversely, sugars
can lead to short-term inhibition of photosynthesis (Foyer 1988) and repress
photosynthetic genes (Sheen 1990; see also Krapp et al. 1991; Schafer et al.
1992). The motif is that carbohydrates - even specific sugars - can act as
"messages" as well as substrates of growth and respiration (Williams and
Farrar 1990). The messages, which are products of photosynthesis and
common forms of carbon translocated from sources to sinks, would coordinate carbon and energy fluxes through photosynthesis and on to growth
and respiration (Fig. 4.4).
79
of metabolism. In support of this generalization, it is commonly observed
that the rate of plant respiration displays a stoichiometric relationship with
the rates of, e.g., growth, translocation, nutrient uptake, and nitrogen
assimilation (Farrar 1985; Amthor 1993b).
4.2.4 Respiration Rate and Carbohydrate Level
A strong positive correlation often exists between plant or tissue carbohydrate content and respiration rate, suggesting that carbohydrate level and
respiration rate are related (Williams and Farrar 1990; Farrar and JHH
Williams 1991; Amthor 1993b). Respiration can be under short-term (minutes to hours) control by ADP availability, however, even though it is
correlated with carbohydrate level over the longer term (Journet et al. 1986;
Brouquisse et al. 1991; Douce et al. 1991). Notably, the addition of sugars
to a tissue increases respiration in the short term when that tissue has been
starved or excised from a supply of endogenous sugars, but not usually
otherwise (ap Rees 1988; Rebeille 1988; Williams and Farrar 1990). Moreover, the relationship between carbohydrate level and respiration rate is
often strongest in growing tissues, and may be absent in mature organs, i.e.,
growth respiration appears to be controlled by carbohydrate level but maintenance respiration does not (Am thor 1989).
It has been inferred that carbohydrates induce processes consuming respiratory products so that over the long term (hours to days) respiration is
positively related to carbohydrate level, but through respiratory control
mechanisms (Bingham and Farrar 1988; Farrar and JHH Williams 1991;
Farrar and ML Williams 1991). For example, an increase in (specific) sugars
may stimulate root nitrate uptake and assimilation (Hanisch ten Cate and
Breteler 1981; Aslam and Huffaker 1984) and perhaps enhance cell division
and differentiation (Williams and Farrar 1990; Farrar and JHH Williams
1991). Each of these increase the demand for carbon skeletons and energy.
Protein levels may be regulated by carbohydrate concentration (Baysdorfer
and van der Woude 1988; Wenzler et al. 1989) with a decrease in cellular
carbohydrate level leading to a loss of respiratory machinery (Journet et al.
1986) and an increase in sugars resulting in increased respiratory capacity
(Ave lange et al. 1990; Farrar and JHH Williams 1991). Conversely, sugars
can lead to short-term inhibition of photosynthesis (Foyer 1988) and repress
photosynthetic genes (Sheen 1990; see also Krapp et al. 1991; Schafer et al.
1992). The motif is that carbohydrates - even specific sugars - can act as
"messages" as well as substrates of growth and respiration (Williams and
Farrar 1990). The messages, which are products of photosynthesis and
common forms of carbon translocated from sources to sinks, would coordinate carbon and energy fluxes through photosynthesis and on to growth
and respiration (Fig. 4.4).