Normally, lignins occurs in hight amount in the secondary plant cell wall. however it can be present in primary cell wall under some defined conditions (such as suspension cells growing under strong light).
Is that means that there will be a continuous process of lignin deposition and subsequently secondary wall formation or this is just a little amount of lignin in the primary wall ?
Hello Mohammad!
I don't think that it's a black-and-white information that if there's a lignin, there will form a secondary cell wall. I think sometimes lignins are synthesized as response to stress (as you have mentioned also) not solely for mechanics. But certainly, it is much correlated that if there is lignin, there would then be a secondary cell wall formation for some mechanical reasons. Thus, if there is a continuous lignin deposition, secondary cell walls usually form.
Here are some papers that might help (disclaimer: I don't own these papers):
Article Secondary Cell Walls: Biosynthesis, Patterned Deposition and...
Article Plant Cell Walls
Hi Mohammed.
In a strict sense, lignified primary cell walls do not normally occur under optimal developmental conditions, but can occur in conditions of stress, where lignification can serve to physically hinder fungal hyphae penetration at the site of infection, e.g. These lignified primary cell walls do not form secondary cell walls, which have a precisely coordinated developmental programme, involving the deposition of several cell wall layers within the primary cell wall after the conclusion of cell elongation and after obtaining the desired cellular width within particular, pre-destined cell lines. In some cases, the developmental programme may be altered due to physical impedance to root or shoot (or branch) growth, causing an altered secondary cell wall development. However, this does not normally occur in cells predestined to remain with a primary cell wall, unless conditions, such as genetic defects, give rise to ectopic lignin deposition. Even in these cases, full secondary cell walls do not usually form (although there may be some evidence I am not aware of).
However, it may also be prudent to remember that many experimental approaches do not distinguish between lignin and lignan accumulation and lignans can have antimicrobial properties, rather than mechanical ones. The functional distinction between lignins and lignans is fuzzy in the first steps in their formation, since Dirigent protein-assisted formation of early lignans may seed lignin formation from the same phenylpropanoid precursors. Both lignins and lignans can be detected in the extracellular matrix. The distinction between lignin and lignans is easier to see at later steps in their formation, where MS techniques, e.g. can detect the formation of more mature lignans, rather than the condensed lignin of secondary cell walls.
I hope that helps,
Phil
thanks Mr. Phil four your accurate and helpful answer. I appreciate it.
Al-salam Alykum Mohamed,
it depends on whether your plant belongs to monocots or dicots.
Generally, the lignification process starts at dicots, which have Type I cell wall, when the cell commit to switch to programmed cell death (PCD), forming the secondary cell wall to initiate xylem vessels. So, lignin doesn't exist at primary cell wall Type I
On the other hand, in Monocots, which have Type II cell wall, Phenylpropanoid compounds are present at Type II primary cell wall.
However, It might be a few exceptions.
Reference: read the book "Biochemistry & molecular biology of plants", Chapter the cell wall.
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