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and increased CO 2 . Increased temperature during the
maturity period of sugarcane may adversely affect the
juice quality, especially juice content; increased summer
drying of the crop could result in substantial yield loss. It
is also possible that there will be an autocatalytic compo-
nent to global warming. Photosynthesis and respiration
of plants and microbes increase with temperature, espe-
cially in temperate latitudes. As respiration increases with
increasing temperatures more than photosynthesis, global
warming is likely to increase the flux of carbon dioxide to
the atmosphere, which would constitute a positive feed-
back to global warming.
7.1 Introduction
To optimise sugarcane improvement, it is necessary to know the
impact a selected trait will have on the general physiology of the
plant. However, this is not yet possible as there are too many gaps
in our knowledge of the unique development and physiology of
sugarcane. Such gaps impair our ability to enhance desired agro-
nomical traits. For example, selection of sugarcane varieties with
increased photosynthetic capacity may be useless if sugar accu-
mulation is constrained by temperature, water deficit or nutrient
availability (Inman-Bamber et al. 2002). It may prove difficult to
consistently increase sucrose levels in the culm without first know-
ing the factors that affect sugarcane yield and carbon partitioning.
A key aspect to increase sugarcane yield is the regulation
of its photosynthetic apparatus. Sugarcane C4 metabolism con-
centrates CO 2 in photosynthetically active tissues, a strategy
that has an energy cost that may be offset by the reduction in
photorespiration rates. There are at least three distinctive forms
of C4 metabolism that can be identified by the decarboxyl-
ation enzymes they use: NADP + -malic enzyme (NADP-ME),
NAD + -malic enzyme (NAD-ME) and phosphoenolpyruvate
carboxykinase (PCK). There is evidence that sugarcane has
both NADP-ME and PCK (Calsa and Figueira 2007), which
suggest the two types of C4 metabolism might complement
each other (Christin et  al. 2007). The physiological implica-
tion of the presence of both pathways and how they could be
explored to increase sugarcane yield is still unknown.
It is also important to detail how carbon demands in the culm
affect photosynthetic rates. Photosynthetic rates decrease with
plant age, which could be a result of physiological limitations to
sucrose accumulation in the culms (McCormick et al. 2006). This
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