Programmed cell death (PCD) processes begin extremely early in Alstroemeria petal senescence

-In the Liliaceous species Alstroemeria, petal senescence is characterized by wilting and inrolling, terminating in abscission 8-10 d after flower opening. -In many species, flower development and senescence involves programmed cell death (PCD). PCD in Alstroemeria petals was investigated by light (LM) and transmission electron microscopy (TEM) (to study nuclear degradation and cellular integrity), DNA laddering and the expression programme of the DAD-1 gene. -TEM showed nuclear and cellular degradation commenced before the flowers were fully open and that epidermal cells remained intact whilst the mesophyll cells degenerated completely. DNA laddering increased throughout petal development. Expression of the ALSDAD-1 partial cDNA was shown to be downregulated after flower opening. -We conclude that some PCD processes are started extremely early and proceed throughout flower opening and senescence, whereas others occur more rapidly between stages 4-6 (i.e. postanthesis). The spatial distribution of PCD across the petals is discussed. Several molecular and physiological markers of PCD are present during Alstroemeria petal senescence. © New Phytologist (2003).

Cysteine protease gene expression and proteolytic activity during senescence of Alstroemeria petals

The functional life of the flower is terminated by senescence and/or abscission. Multiple processes contribute to produce the visible signs of petal wilting and inrolling that typify senescence, but one of the most important is that of protein degradation and remobilization. This is mediated in many species through protein ubiquitination and the action of specific protease enzymes. This paper reports the changes in protein and protease activity during development and senescence of Alstroemeria flowers, a Liliaceous species that shows very little sensitivity to ethylene during senescence and which shows perianth abscission 8-10 d after flower opening. Partial cDNAs of ubiquitin (ALSUQ1) and a putative cysteine protease (ALSCYP1) were cloned from Alstroemeria using degenerate PCR primers and the expression pattern of these genes was determined semi-quantitatively by RT-PCR. While the levels of ALSUQ1 only fluctuated slightly during floral development and senescence, there was a dramatic increase in the expression of ALSCYP1 indicating that this gene may encode an important enzyme for the proteolytic process in this species. Three papain class cysteine protease enzymes showing different patterns of activity during flower development were identified on zymograms, one of which showed a similar expression pattern to the cysteine protease cDNA.