POTATO PLANTS CONTAIN MULTIPLE FORMS OF SUCROSE-PHOSPHATE SYNTHASE, WHICH DIFFER IN THEIR TISSUE DISTRIBUTIONS, THEIR LEVELS DURING DEVELOPMENT, AND THEIR RESPONSES TO LOW-TEMPERATURE
R. Reimholz et al., POTATO PLANTS CONTAIN MULTIPLE FORMS OF SUCROSE-PHOSPHATE SYNTHASE, WHICH DIFFER IN THEIR TISSUE DISTRIBUTIONS, THEIR LEVELS DURING DEVELOPMENT, AND THEIR RESPONSES TO LOW-TEMPERATURE, Plant, cell and environment, 20(3), 1997, pp. 291-305
Antibodies raised against a peptide fragment (residues 60-456) of pota
to sucrose phosphate synthase (SPS) were used to investigate whether p
otato plants contain multiple forms of SPS. When a partially purified
preparation of SPS from cold-stored potato tubers was separated on 5%
polyacrylamide gel electrophoresis (PAGE), four immunopositive bands w
ere found with estimated molecular weights of 125, 127, 135 and 145 kD
a. These bands were also found in rapidly prepared extracts and were t
ermed SPS-1a, SPS-1b, SPS-2 and SPS-3, respectively. Direct evidence t
hat SPS-1a and SPS-1b represent active SPS was provided by the finding
that both are greatly reduced in plants expressing an antisense seque
nce derived from the potato leaf SPS gene. SPS-2 was not decreased in
the antisense plants, indicating that it has a significantly different
sequence. Evidence that SPS-2 represents active SPS was obtained by s
howing that the amount of SPS-1a and SPS-1b protein remaining in the l
eaves and tubers of antisense potato plants was too low to account for
the remaining SPS activity. The four immunopositive SPS forms had dif
ferent tissue distributions. SPS-1a was the major form in all tissues
except petals, sepals and stamens. SPS-1b and SPS-2 were absent in ver
y young growing tissues but were present as minor forms in source leav
es and sprouting tubers. The SPS-1b level was especially high in petal
s and sepals, and the SPS-2 level was especially high in the stamens.
SPS-3 was only detected in very young tissues. The four forms also sho
wed different responses to low temperature. Transfer of tubers to 4 de
grees C led to a specific and reversible increase of SPS-1b during the
next 4 d. The appearance of SPS-1b correlated with a change in the ki
netic properties of SPS that has recently been shown (Hill et al. 1996
) to play a key role in triggering the accumulation of sugars in cold-
stored tubers. The appearance of SPS-1b protein at low temperature was
accompanied by an increase of SPS transcript. Incubation of tuber sli
ces with calyculin A and okadaic acid to alter the phosphorylation sta
te of SPS did not lead to appearance or disappearance of SPS-1b. It is
concluded that potato plants contain several forms of SPS that have d
ifferent functions in growing and mature tissues, in flower parts, and
in acclimation to low temperature.