Pakistan Sugar Journal

thaliana and Sp/'nocio oleracea PRS4, respectively. The assignment of sugarcane PRS as a
phosphate-independent PRS isoenzyme (Class II PRS) is verified following enzyme assay
and phylogenetic reconstruction of PRS homologues. To gain further insight into the
structural framework of the phosphate independence of sugarcane PRS, a molecular model is
described. This model reveals the formation of two conserved domains elucidating the
structural features involved in sugarcane PRS phosphate independence. The recombinant
PRS retains secondary structure elements and a quaternary arrangement consistent with
known PRS homologues, based on circular dichroism measurements.
Estimating sugarcane root length density through root mapping and orientation modelling
Jean-Louis Chopart, Silvia Rosa Rodrigues, Mateus Carvalho de Azevedo and Cristiane de
Conti Medina
Root length density (RLD) is a key factor in crop functioning. A field method was developed
to quantify RLD of sugarcane from root intersection density (RID) taking root orientations
into account. RIDs were observed on three perpendicular soil planes and RLD was measured
for the enclosed volume. RID and RLD of thick and fine roots were measured separately.
These measurements were replicated at different ages and sites to test models describing
RLD according to RID. Fine roots were nearly isotropic and thick roots had a preferential
orientation, i.e. horizontal near the surface and becoming progressively vertical in deeper
horizons. Relationships in thick roots were modelled according to CO t : RLD t = RID t . CO t
(CO t : root orientation coefficient, ranged from 1.3 to 4.9 for thick roots). For fine roots ( f ),
CO f =2.This theoretical model led to differences between measured and calculated RLD.The
ratio between measured and calculated RLD f (CE f ) increased from I to 3 with RID f . CEj was
introduced as an additional coefficient in the model: RLD f =2. Nl f . CEf. Intermediate results
were obtained for all (a) roots: CO a and CEa were both dependent on RID a , therefore: RLD a
= Nl a . CO a . CE a . The models were validated with independent datasets from Brazil and
France. These allowed a more robust prediction of RLD than direct regressions between RID
and RLD. They may estimate RLD from RID in soil profiles by root mapping while taking
RLD spatial variability into account.
The reduction of starch accumulation in trans-genic sugarcane cell suspension culture
lines
Stephanus J. Ferreira, Jens Kossmann, James R. Lloyd, Jan-Hendrik Groenewald,
Starch only occurs in small amounts in sugarcane, but is, nevertheless an unwanted product
because it reduces the amount of sucrose that can be crystallized from molasses. In an attempt
to reduce the starch content of sugarcane, the activities of ADP-glucose pyrophos-phorylase
(AGPase) and (3-amylase were manipulated using trans-genic approaches. Transformation
vectors to reduce AGPase activity and to increase plastidial p-amylase activity were
constructed and used for the transformation of sugarcane calli. The results of the
manipulations were analyzed in suspension cultures. AGPase activity was reduced down to
between 14 and 54% of the wild-type control. This led to a reduction in starch concentration
down to 38% of the levels of the wild-type control. (5-Amylase activity was increased in the
transgenic lines by 1.5-2 times that of the wild-type control. This increase in activity led to a
reduction in starch amounts by 90% compared to wild-type control cells. In both
experiments, the changes in starch concentrations could be correlated with the change in
enzyme activity. There were no significant effects on sucrose concentrations in either
experiment, indicating that these approaches might be useful to engineer regenerated