PHYTOHORMONES IN NEEDLES OF HEALTHY AND DECLINING SILVER FIR (ABIES-ALBA MILL) .3. ETHYLENE - THE IMMEDIATE ETHYLENE PRECURSOR 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID AND ITS MALONYL CONJUGATE
A. Christmann et B. Frenzel, PHYTOHORMONES IN NEEDLES OF HEALTHY AND DECLINING SILVER FIR (ABIES-ALBA MILL) .3. ETHYLENE - THE IMMEDIATE ETHYLENE PRECURSOR 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID AND ITS MALONYL CONJUGATE, Journal of plant physiology, 150(3), 1997, pp. 271-278
Levels of the immediate ethylene precursor 1-aminocyclopropane-1-carbo
xylic acid (ACC) and its conjugate N-malonyl-ACC (MACC) were determine
d in needles belonging to different age classes of healthy and declini
ng silver fir trees (Abies alba Mill.) in the northern Black Forest, G
ermany. Levels of MACC in fir needles exhibited a seasonal trend with
a maximum in winter and a minimum in spring just before budbreak, wher
eas no common seasonal trend was seen in levels of ACC. Levels of ACC
and MACC were found to be elevated in declining trees several times, i
ndicating that ethylene production in such trees is temporarily enhanc
ed. During a prolonged period with restricted water availability from
the soil, however, declining trees produced less ACC and MACC. As indi
cated by needle levels of abscisic acid (ABA; Christmann et al., 1995)
, these trees had suffered from severe water stress while healthy tree
s had experienced only moderate water stress. It is concluded that the
formation of ACC is inhibited in trees that: experience severe water
stress, and therefore, less MACC accumulates. Levels of MACC may thus
serve as a measure of tree health status only when severe water stress
is absent. Levels of ACC rose with increasing needle age, indicating
that ethylene production is high in older needles. Since levels of ind
ole-3-acetic acid were high in older needles of healthy trees but low
in older needles of declining trees (Christmann et al., 1996), prematu
re needle loss of declining trees is probably caused by an enhanced pr
oduction of ethylene in needles that are not protected by high levels
of IAA. The possible factors that temporarily enhance ethylene product
ion in declining fir trees are discussed.