Physiology of Stem "Ripening" and rooting

Rod Savidge savidge at unb.ca
Mon Aug 20 09:44:55 EST 2001


Bernard,
Completion of lignification of xylem (and phloem fibres in some species) 
definitely is associated with the firming up process, but lignification 
and/or suberisation of cortical cells also contributes.  Cortical 
parenchyma can transform into suberised collenchyma or differentiate into 
sclerenchyma.   In many species close examination reveals that pith 
parenchyma also thicken and lignify as they age.   Lignification or 
suberisation of the epidermis may enhance the firmness.

I agree that cuttings of many species root better once they've firmed up 
(poplars are a good example).  On the other hand, firm cuttings of others 
will not root at all (many species could be listed: You might want to look 
at a text like Plant Propagation by Hartmann and Kester).   At least some 
species will root despite still being tender, if kept under mist in a warm 
rooting bed.   Root induction of  'soft' stems is enhanced if you debud and 
have mature (as opposed to enlarging) leaves present.     Truly generic 
principles for rooting of woody plants remain wanting; those which are 
difficult to root generally are grafted for propagation purposes.

Rod Savidge

At 10:30 AM 8/20/01 +0100, you wrote:
>I am currently researching the literature relating to processes that
>take place in woody stems as new growth firms up following a flush of
>growth.  Currently my level of understanding is as follows,
>i) New growth of cells stage one, all cells parenchyma in nature
>ii) Thickening of some cells in stem i.e. formation of collenchyma cells
>resulting from lay down of some secondary cell wall polysaccharides, all
>stem support due to turgor pressure
>iii) Lignification of cell walls in a range of tissues, yielding
>structural support.
>
> From experience I know that woody cuttings do not root readily if at all
>until they have passed through the "rubbery feel" stage to a firmer
>stage.  My question is does this "ripening" equate with formation of
>adequate lignin needed to support stem tissues and so complete a stage
>of the vegetative tisues growth phase?.
>Also is collenchyma cell production a stage in the production of
>lignified cell in woody plants?. comments appreciated
>B. Brennan
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